Room Air Conditioners Repair

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Room Air Conditioners

Room air conditioners (RACs) are available in different sizes (rated in BTUs) and

cabinet styles.1 These units can be installed in a window or through the wall, or are

available as a portable unit on wheels (Figure 1-16). Manufacturers have designed

RACs with electromechanical controls or electronic controls. Consumers can purchase an

RAC that is straight cool only, cool with heat (electric), heat pump (reverse cycle), or a

combination of cool and heat (electric heat and reverse cycle).

The room air conditioner consists of the following:

• The base pan, fan housing, divider section (bulkhead), and outer cabinet

• The sealed system, which consists of the evaporator coil, the condenser coil, the

compressor, and the connecting tubing

• The electrical circuitry, including the fan motor and other electrical components

Principles of Operation

The room air conditioner, when installed and running properly, will circulate the air in a

room or area, removing the heat and humidity; some models will heat the air in the winter

months. At the same time, the air filter, located behind the front grille, will filter out dust

particles. Most models have a fresh air intake feature, which allows fresh outside air to enter

the room when the unit is running. The thermostat will control the comfort level in the

room or area, and cycle the air conditioner on and off according to the temperature setting.

Before continuing, take a moment to refresh your memory of Chapter 9. These two

chapters combined will make servicing room air conditioners a breeze.

Safety First

Any person who cannot use basic tools or follow written instructions should not attempt to

install, maintain, or repair any room air conditioners. Any improper installation, preventive

maintenance, or repairs could create a risk of personal injury or property damage. If you do

not fully understand the installation, preventive maintenance, or repair procedures in this

chapter, or if you doubt your ability to complete the task on your room air conditioner,

please call your service manager.

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This chapter covers the electrical components and how to diagnose the sealed system.

The actual repair or replacement of any sealed-system component is not included in this

chapter. It is recommended that you acquire refrigerant certification (or call an authorized

service company) to repair or replace any sealed-system component, as the refrigerant in

the sealed system must be recovered properly.

Before continuing, take a moment to refresh your memory on the safety procedures in

Chapter 2.

Room Air Conditioners in General

Much of the troubleshooting information in this chapter covers room air conditioners in

general, rather than specific models, in order to present a broad overview of service

techniques. The illustrations that are used in this chapter are for demonstration purposes

only, to clarify the description of how to service these appliances. They in no way reflect on

a particular brand’s reliability.

Electrical Requirements

One of the most common problems that I have encountered over the years is when a

consumer plugs the room air conditioner into an existing 115-volt receptacle only to find out

that the circuit breaker keeps tripping. Most people do not take into account that this

receptacle is connected to the other receptacles and/or lights in the same room and on the

same branch circuit. This means that there is a limit to how many items can be connected to

one branch circuit. Before a consumer purchases a room air conditioner, he or she needs to

add up the total amperage or wattage of the items that are plugged into the branch circuit

where the air conditioner is going to be plugged in. For example, on a 15-amp circuit, the

total wattage on a 120-volt circuit should not exceed 1800 watts (Table 29-1). For safety

Circuit Breaker Size

Rated in Amps Volts Watts BTUs

15 120 1800 6138

20 120 2400 8184

25 120 3000 10,230

30 230 6900 23,529

40 230 9200 31,372

50 230 11,500 39,215

60 230 13,800 47,058

70 230 16,100 54,901

80 230 18,400 62,744

100 230 23,000 78,430

Conversion formulas: Watts = Volts x Amps; BTUs = Watts x 3.41; Amps = Watts/Volts

TABLE 29-1 Conversion Formulas for Amps, Volts, Watts, and BTUs

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reasons, all of the items, including the air conditioner, should stay below the amperage

rating on the circuit breaker by 20 percent. The 115-volt, 15-amp circuit is reserved for lights,

computers, televisions, stereos, etc. The 115-volt, 20-amp circuit is reserved for a refrigerator,

dishwasher, automatic washer, or a garbage disposer only. Most 230-volt, 15- to 60-amp

receptacles are on a single branch circuit. Figure 29-1 illustrates the type of plug connections

needed for a room air conditioner. All room air conditioners and portable air conditioners

must have a properly polarized and grounded receptacle, with the correct operating voltage

for the unit purchased, preferably on its own branch circuit (Table 29-2). If the consumer

only has multiple receptacles on one branch circuit, advise him or her to calculate the total

amperage or wattage of each item (for example: television, computer, printer, computer

monitor, lamps, microwave oven, etc.). Advise the consumer not to exceed the rated branch

circuit, circuit breaker, or fuse. If the consumer does not correct the problem, this could lead

to a possible fire hazard if the home wiring overheats.

Location and Installation of Room Air Conditioner

Room air conditioners and portable models can be installed in various types of windows

(Figures 29-2 and 29-3) or through the wall (Figure 29-4) for permanent installation. It is the

installer’s responsibility to make sure that the air conditioner is installed properly according

to the manufacturer’s specifications and local building codes. If the air conditioner is

installed in a window, the installer must make sure that the air conditioner is secured to the

window so that it will not fall out, causing injury, death, or property damage. Through-thewall

models should be secured to the wall to prevent the unit from being pushed out of the

FIGURE 29-1

An electrical

receptacle guide

illustrating the type of

receptacle needed for

the amperage rating.

TABLE 29-2 The Minimum/Maximum Operating Voltages for an Air Conditioner

Operating Voltages Minimum Voltages Maximum Voltages

115 104 127

120 108 132

208 188 229

220 198 242

230 207 253

240 216 264

115 volt

not grounded.

Not

recommended.

230 volt

grounded

15 amp

230 volt

grounded

20 amp

115 volt

grounded

15 amp

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wall when the unit is installed or serviced. Portable air conditioners are much easier to

install. The air intake and discharge hoses are installed through a small opening in the

window. This type of unit can be moved around from room to room easily.

The following are some helpful tips when considering a location to install a window air

conditioner:

• Make sure you have the correct size (BTUs) for the area being cooled.2

• When selecting an air conditioner, make sure that the air vents will be able to point

to the center of the room for better air circulation.

Double-hung Casement Sliding Awning Transom above

a doorway

Types of windows

FIGURE 29-3

A typical portable air

conditioner

installation.

FIGURE 29-2 Room air conditioners can be installed in these types of windows. When selecting an air

conditioner to purchase, measure the window opening.

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FIGURE 29-4

(a) A typical wall

installation. The air

conditioner must be

installed with a slight

pitch so that the

condensate water can

drain to the rear of

the unit. (b) If the

outside vents cannot

clear the wall

structure, purchase an

air conditioner with a

sleeve without side

vents.

The cabinet vents must

clear the exterior wall for

maximum air circulation.

(a)

Through-the-wall

air conditioner

Wall sleeve

Rear grille

Some models have

no side vents. The

outside air is drawn

into the rear and

discharged through

the rear.

(b)

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• When purchasing a window air conditioner, purchase one that is designed for the

type of window in the home (see Figure 29-2). This will make for an easier

installation.

• Make sure the unit will fit the window opening. Measure the opening of the

window.

• Check the electrical outlet voltage. The voltage should match the operating voltage

of the unit being installed.

• The electrical outlet should not be farther away than the length of the service cord.

• For larger air conditioners, install the brackets that come with the air conditioner.

These brackets will reduce the stress on the window.

• Make sure there is adequate airflow with no obstructions on the outside of the

building.

• Do not install a room air conditioner in an area where the temperature will exceed

120 degrees Fahrenheit.

The following are some helpful tips when considering a location to install a throughthe-

wall air conditioner:

• Make sure you have the correct size (BTUs) for the area being cooled.2

• When selecting an air conditioner, make sure that the air vents will be able to point

to the center of the room for better air circulation.

• Measure the depth of the wall where the air conditioner will be installed. Make sure

that the outside louvers will not be blocked (see Figure 29-4).

• Purchase an air conditioner with a slide-out chassis or with a wall sleeve for easier

installation.

• Check the electrical outlet voltage. It should match the operating voltage of the unit

being installed.

• The electrical outlet should not be farther away than the length of the service cord.

• Make sure there is adequate airflow with no obstructions on the outside of the

building.

• Do not install a room air conditioner in an area where the temperature will exceed

120 degrees Fahrenheit.

Step-by-Step Troubleshooting by Symptom Diagnosis

When servicing an air conditioner, don’t overlook the simple things that might be causing

the problem. Step-by-step troubleshooting by symptom diagnosis is based on diagnosing

malfunctions, with possible causes arranged into categories relating to the operation of

the room air conditioner. This section is intended only to serve as a checklist to aid you in

diagnosing a problem. Look at the symptom that best describes the problem you are

experiencing with the air conditioner, and then correct the problem.

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Air Conditioner Will Not Run

• Is the unit service cord plugged in?

• Check for voltage at the receptacle.

• Are the controls set properly?

• Check for a blown fuse or tripped circuit breaker. Check for total wattage on the

branch circuit.

• Check the selector switch or electronic control board.

• Check all wiring connections and wiring.

Air Conditioner Will Not Cool or Cools Slightly

• Check for a dirty filter.

• Check for a dirty or restricted evaporator coil.

• Check for a dirty or restricted condenser coil.

• Check fan speed setting. Are the louvers adjusted correctly?

• Check the thermostat setting.

• Check the refrigeration cycle for leaks or an undercharge.

• Is the air conditioner the right size for the area to be cooled?2

• Is the fresh air intake or exhaust door open?

Compressor Will Not Run

• Check for the correct voltage at the receptacle.

• Check the control settings.

• Check the wiring connectors and wiring.

• Check the thermostat setting.

• Check the selector switch or electronic control board.

• Test the compressor for an open, short, or grounded winding.

• Test the overload.

• Test the compressor capacitor for an open, short, or ground.

Fan Motor Will Not Run

• Check the fan selector switch, main selector switch, or electronic control board.

• Check the wiring connectors and wiring.

• Test the fan capacitor for an open, short, or ground.

• Test the fan motor windings for an open, short, or ground.

Evaporator Coil Freezes Up

• Check for a dirty filter.

• Check for a dirty or restricted evaporator coil.

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• Check the thermostat.

• Check fan motor.

• Check the refrigeration cycle for leaks, undercharge, or capillary tube restriction.

Condenser Coil Frozen (Heat Pump Models Only)

• Check defrost thermostat (outdoor thermostat) switch contacts and the capillary

tube placement.

• Check the solenoid coil on the reversing valve.

• Check the reversing valve.

• Check the control settings.

Compressor Runs Continually and Will Not Cycle Off

• Check for excessive heat load. Is the air conditioner the right size for the area to be

cooled?2

• Check for a partial refrigeration restriction in the line. Is the evaporator coil partially

iced up?

• Check for a refrigerant leak.

• Check the running amperage against the model number identification plate on the

air conditioner.

• Check the thermostat for proper operation.

Thermostat Will Not Cycle Off the Air Conditioner

• Check for stuck thermostat contacts.

• Check the thermostat setting.

• Check the wiring connections. Is the thermostat wired correctly?

• Is the air conditioner the right size for the area to be cooled?2

Thermostat Will Not Cycle the Air Conditioner On

• Check the thermostat bulb and capillary tube for loss of charge.

• Test the thermostat.

• Check the wiring connections and wiring.

• Check the control settings.

Thermostat Will Short-Cycle

• Is the air conditioner the right size for the area to be cooled?2

• Check for a dirty or restricted evaporator coil.

• Check for a dirty filter.

• Check the positioning of the thermostat bulb. Test the thermostat differential.

• Check and make sure that the plenum gasket is sealing properly.

• Check for outside air leakage into the air conditioner.

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Compressor Runs and then Cycles on Overload

• Check for low voltage at the receptacle.

• Check the compressor overload.

• Did the compressor restart before the sealed system had a chance to equalize?

Advise the customer to wait about three or four minutes after the air conditioner

cycles off before restarting the compressor.

• Check the wiring connections and wiring.

• Check the compressor capacitor for an open, short, or ground.

• Check for a dirty or restricted condenser coil.

• Check the amperage of the air conditioner.

• Check for a kinked discharge line.

Air Conditioner Is Noisy

• Check the air conditioner installation.

• Make sure the fan blade and blower wheel are not striking the chassis.

• Check the compressor mounts and tubing.

• Inspect for loose cabinet parts.

Water Leaks Inside the Home

• Check the evaporator drain pan and drain for a blockage.

• Check weather sealing around the outer cabinet. Reseal if necessary.

• Check for water droplets on the outside of the base pan. If so, the evaporator drain

pan might be cracked. Inspect the evaporator drain pan.

• Check the back side of the discharge grille. If it is wet, the evaporator coil might

be dirty.

• Inspect all gaskets between the unit, outer cabinet, and window panes for air leakage.

• Check the angle of slope on the air conditioner installation.

• Check for a dirty evaporator coil.

Water Leaks on the Outside of the Home

• Check for water droplets on the outside of the base pan. If so, the evaporator drain

pan might be cracked. Inspect the evaporator drain pan.

• Check for water between the condenser fan shroud and the compressor. If the water

has collected around the compressor, inspect the fan shroud. Is it detached from the

condenser coil?

• Check for a dirty condenser coil.

• Inspect the condenser fan blade—is the slinger ring in the correct position?

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Air Conditioner Will Not Heat or There Is Not Enough Heat

• On electric heat models, check the electric heater and thermostats.

• On heat pump models, check the reversing valve, reversing valve solenoid coil, and

thermostats.

• Check for a dirty filter.

• Check for an open fresh air intake or exhaust vent.

• Is the air conditioner the right size for the area?2

• Check for a dirty evaporator coil.

• Check the wiring connections and wiring.

• Check selector switch or electronic control board.

Heat Pump Will Not Go Into Defrost

• Check the defrost control and thermostats.

• Check the reversing valve and solenoid coil.

• Check the wiring connections and wiring.

• Check the electronic control board.

Air Conditioner Is Cooling When the Controls Are Set for Heat

• Check the wiring connections and wiring.

• Check the reversing valve and solenoid coil.

• Check the selector switch or electronic control board.

• Check the thermostats.

Room Air Conditioner Maintenance

Room air conditioners (including portable models) have air filters that need cleaning every

225 to 360 fan-hours of operation. The discharge grille area also needs vacuuming to remove

the dust buildup. Twice a year, the following areas need to be inspected and cleaned:

• The evaporator coil

• The condenser coil

• The evaporator pan and base pan

• The indoor blower housing and blower wheel

• All the wiring connections and wiring

• The electrical and mechanical controls

• The voltage at the receptacle

• The inside and outside of the air conditioner

• All gaskets

• The drain system (clean it, too)

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• The cabinet seal (clean the outer cabinet)

• The copper tubing

Twice a year you must inspect all control components: electrical and mechanical, electronic,

as well as the power supply. The technician must use the proper testing instruments (voltmeter,

ohmmeter, ammeter, wattmeter, etc.) to perform electrical tests. The technician should also

use an air conditioner or refrigeration thermometer to test the room, outdoor, and coil

operating temperatures. Use a sling psychrometer to measure the wet bulb temperatures

indoors and outdoors.

When cleaning the air conditioner, use an approved cleaner to wash the unit. Remember

to protect the electrical components and fan motor with plastic to prevent the water from

damaging the components. Refer to the use and care manual that comes with every air

conditioner for further maintenance instructions on the model you are servicing. Do not

plug in or run the air conditioner after using water to clean the unit. Wait a few hours,

allowing the air conditioner to completely dry out. To prevent electrical mishaps, the air

conditioner must be totally dry before you can plug it in.

Performance Data

After you have completed the maintenance or repair on the air conditioner, perform an

electrical test by checking the amperage or wattage on the unit, and compare the readings

with the information on the model number data tag. At the same time, perform readings on

the following:

• The room temperature and outside temperature.

• The temperature differential of the intake and discharge air through the evaporator

coil. Take a reliable thermometer, place it in front of the air intake (where the air filter

is located), and take a reading. Then place the thermometer in the discharge grille,

and take a reading of the air blowing into the room. The difference between the two

readings will be the temperature drop. This reading will vary among manufacturers

and models. The temperature drop should be between 18 and 31 degrees Fahrenheit.

• The temperature differential of the intake and discharge air through the condenser

coil. Use the same reliable thermometer to take the readings.

• Use a sling psychrometer to measure the indoor and the outdoor wet bulb

temperatures. The sling psychrometer will measure the relative humidity in the

room and outside (Table 29-3).

• Measure the operating voltage.

• Measure the startup and cycling amperage or wattage of the unit.

Take the readings and match them against the manufacturer’s performance data. You

can locate the air conditioner performance data on the manufacturer’s Web site or in the

manufacturer’s service manual. The data that you accumulated should match—if it doesn’t,

adjustments will have to be made to bring the air conditioner up to manufacturer’s standards.

You might have to replace a component, clean the unit, or correct the installation.

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Repair Procedures

Each repair procedure is a complete inspection and repair process for a single room air

conditioner component. It contains the information you need to test and replace components.

Electronic Components

The electronic components consist of the following: electronic control board, touchpad, and

remote control unit.

Temperature

of the Room

or Outside (Dry

Bulb) in Degrees

Fahrenheit

The Temperature Difference Between the Dry Bulb and the Wet Bulb

Temperatures in Degrees Fahrenheit

4 5 6 7 8 9 10 11 12

Relative Humidity % at Pressure = 30.00 Inches

40 68 60 52 45 37 29 22 15 7

50 74 67 61 55 49 43 38 32 27

52 75 69 63 57 51 46 40 35 29

54 76 70 64 59 53 48 42 37 32

56 76 71 65 60 55 50 44 39 34

58 77 72 66 61 56 51 46 41 37

60 78 73 68 63 58 53 48 43 39

62 79 74 69 64 59 54 50 45 41

64 79 74 70 65 60 56 51 47 43

66 80 75 71 66 61 57 53 48 44

68 80 76 71 67 62 58 54 50 46

70 81 77 72 68 64 59 55 51 48

72 82 77 73 69 65 61 57 53 49

74 82 78 74 69 65 61 58 54 50

76 82 78 74 70 66 62 59 55 51

78 83 79 75 71 67 63 60 56 53

80 83 79 75 72 68 64 61 57 54

82 84 80 76 72 69 65 61 58 55

84 84 80 76 73 69 66 62 59 56

86 84 81 77 73 70 66 63 60 57

88 85 81 77 74 70 67 64 61 57

90 85 81 78 74 71 68 65 61 58

100 86 83 80 77 73 70 68 65 62

TABLE 29-3 Psychrometric Table. A Wet Bulb Depression Chart. Formula: DB – WB = WDB

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The typical complaints associated with the electronic components are:

• Unable to program the touchpad panel functions.

• The display board will not display anything.

• Unusual display readouts.

• Unable to control the temperatures.

• The compressor will not run.

• The fan motor will not run.

To prevent electrostatic discharge (ESD) from damaging expensive electronic components,

follow the steps in Chapter 11.

To handle these problems, perform the following steps:

1. Verify the complaint. Verify the complaint by operating the air conditioner controls.

Turn off the electricity to the air conditioner, and wait for two minutes before turning

it back on. If a fault code appears, look up the code. If the air conditioner will not

power up, locate the technical data sheet behind the control panel for diagnostics

information. It will be helpful if you can locate the actual service manual for the air

conditioner model you are working on to properly diagnose the air conditioner. The

service manual will assist you in properly placing the air conditioner in the service

test mode for testing the air conditioner functions.

2. Check for external factors. You must check for external factors not associated with

the air conditioner. Is there electricity to the air conditioner? The voltage at the wall

receptacle must be within ±10 percent of the voltage rating on the model and serial

data plate. Do you have the correct polarity? (See Chapter 6.) Is the electrical

receptacle polarized and properly grounded?

3. Disconnect the electricity. Before working on the air conditioner, disconnect the

electricity. This can be done by pulling the plug out of the wall receptacle. Or disconnect

the electricity at the fuse panel or circuit breaker panel. Turn off the electricity.

WARNING Some diagnostic tests will require you to test the components with the power turned on.

When you disassemble the control panel or remove the outer cabinet, you can position the panel

in such a way that the wiring will not make contact with metal. This will allow you to test the

components without electrical mishaps.

4. Gain access to the electronic components. You can gain access to the electronic

components by removing the front grille and the screws on the control panel. Some

units have either a one-piece or a two-piece grille with locking tabs and/or screws

(Figure 29-5). Be careful not to break the tabs on the grille. On window models, you

might have to remove the air conditioner from the window to gain access to the

controls. On other models, you should be able to gain access by removing the screws

that secure the control panel to the air conditioner frame. Next, tilt the control panel

away from the air conditioner, making sure not to pull any of the wires off the controls.

WARNING Do not touch the wiring or capacitor until it is discharged.

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WARNING A capacitor will hold a charge indefinitely, even when it is not currently in use. A

charged capacitor is extremely dangerous. Discharge all capacitors immediately any time that

work is being conducted in their vicinity. Redischarge after repowering the equipment if further

work must be done. Many capacitors are internally fused. If you are not sure, you can use a

20,000 ohm 2-watt resistor to discharge the capacitor. Do not use a screwdriver to short out the

capacitor. By doing so, you will blow out the fuse in the capacitor and the capacitor will not

work. Safely use an insulated pair of pliers to remove the wires from the capacitor and place the

resistor across the capacitor terminals. When checking a dual capacitor with a capacitor analyzer

or ohmmeter, you must test both sides of the capacitor.

5. Test the electronic components. If you are able to run the air conditioner test mode,

check the different functions of the air conditioner. Use the technical data sheet for

the model you are servicing to locate the test points on the wiring schematic. Check

all wiring connections and wiring. Using the technical data sheet, test the electronic

control and display board, input voltages, and output voltages.

6. Remove the defective component. To remove the defective component, remove the

screws that secure the printed circuit board to the air conditioner frame. Disconnect

the connectors from the electronic control board and display.

7. Install the new component. To install a new component, just reverse the disassembly

procedure, and reassemble. Reinstall all panels and the front grille, and restore the

electricity to the air conditioner. Test the room air conditioner operation. To prevent

ESD from damaging expensive electronic components, simply follow the steps in

Chapter 11.

(a) (b)

FIGURE 29-5 On some models, the air ilter can be removed by sliding it out of the unit or by removing the

front grille. Be careful not to damage the tabs on the grille.

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Thermistor

The thermistors used in the electronic models plug into the electronic control board, and

they monitor the ambient and outdoor temperatures and troubleshooting capabilities.

The typical complaints associated with failure of the thermistor are:

• The air conditioner will not cool or heat.

• Erratic temperature control.

• The air conditioner doesn’t run at all.

To handle these problems, perform the following steps:

1. Verify the complaint. Verify the complaint by checking the control setting. Turn the

control to the lowest setting for cool or the highest setting for heat; then turn it back

to a normal setting to see if the air conditioner starts cooling or heating. It will be

helpful if you can locate the actual service manual for the air conditioner model you

are working on to properly diagnose the air conditioner. The service manual will

assist you in properly placing the air conditioner in the service test mode for testing

the air conditioner functions.

2. Check for external factors. You must check for external factors not associated with

the air conditioner. Is the air conditioner installed properly? Is the exhaust or fresh

air intake vent open? Explain to the user how to set the controls. The voltage at the

wall receptacle must be within ±10 percent of the voltage rating on the model and

serial data plate. Do you have the correct polarity? (See Chapter 6.)

3. Disconnect the electricity. Before working on the air conditioner, disconnect the

electricity to the unit. This can be done by pulling the plug from the receptacle. Or

disconnect the electricity at the fuse panel or at the circuit breaker panel. Turn off

the electricity.

4. Gain access to the thermistor. To access the thermistor, remove the front grille and

filter. Some units have either a one-piece or a two-piece grille with locking tabs

and/or screws (see Figure 29-5). Be careful not to break the tabs on the grill. On

window models, you might have to remove the air conditioner from the window to

gain access to the controls. On other models, you should be able to gain access by

removing the screws that secure the control panel to the air conditioner frame. Next,

tilt the control panel away from the air conditioner, making sure not to pull any of

the wires off the controls.

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WARNING Do not touch the wiring or capacitor until it is discharged. A capacitor will hold

a charge indefinitely, even when it is not currently in use. A charged capacitor is extremely

dangerous. Discharge all capacitors immediately any time that work is being conducted in their

vicinity. Redischarge after repowering the equipment if further work must be done. Many

capacitors are internally fused. If you are not sure, you can use a 20,000 ohm 2-watt resistor to

discharge the capacitor. Do not use a screwdriver to short out the capacitor. By doing so, you will

blow out the fuse in the capacitor and the capacitor will not work. Safely use an insulated pair of

pliers to remove the wires from the capacitor and place the resistor across the capacitor terminals.

When checking a dual capacitor with a capacitor analyzer or ohmmeter, you must test both sides

of the capacitor.

5. Test the thermistor. The thermistor is attached to the evaporator coil; trace the

thermistor wire back to the electronic control board. Disconnect the thermistor

connector from the board. Set the ohmmeter on R × 10K, and place the probes on

the connector pin terminals. Measure the resistance of the thermistor. Using the

technical data sheet, look for the reading and see if the results match. The reading

can vary ±10 percent on the chart. Remove the thermistor from the evaporator coil,

and submerge the thermistor in ice water for five minutes—the resistance will

increase. As the thermistor warms up to ambient temperature, the resistance should

return to the original reading. If you suspect an erratic thermistor, replace it with a

duplicate of the original.

6. Install a new thermistor. To install the new thermistor, just reverse the order of

disassembly, and reassemble. Then test the thermistor. Remember to reinstall the

sensor in the same location from which it was removed. If you do not, the air

conditioner will not cycle properly.

Thermostat (Operating)

The operating thermostat is located in the control panel. The operating thermostat

monitors the ambient room temperature and cycles the air conditioner on and off.

The typical complaints associated with failure of the thermostat are:

• The air conditioner will not cool enough.

• The room or area is too cold.

• The air conditioner runs all the time.

• The air conditioner doesn’t run at all.

To handle these problems, perform the following steps:

1. Verify the complaint. Verify the complaint by checking the control setting. Turn the

control to the lowest setting for cool or the highest setting for heat; then turn it back

to a normal setting to see if the air conditioner starts cooling or heating. It will be

helpful if you can locate the actual service manual for the air conditioner model you

are working on to properly diagnose the air conditioner.

2. Check for external factors. You must check for external factors not associated with

the air conditioner. Is the air conditioner installed properly? Is the exhaust or fresh

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air intake vent open? Explain to the user how to set the controls. The voltage at the

wall receptacle must be within ±10 percent of the voltage rating on the model and

serial data plate. Do you have the correct polarity? (See Chapter 6.)

3. Disconnect the electricity. Before working on the air conditioner, disconnect the

electricity to the unit. This can be done by pulling the plug from the receptacle. Or

disconnect the electricity at the fuse panel or at the circuit breaker panel. Turn off

the electricity.

4. Gain access to the thermostat. To access the thermostat, remove the front grille and

filter. Some units have either a one-piece or a two-piece grille with locking tabs

and/or screws (see Figure 29-5). Be careful not to break the tabs on the grille. On

window models, you might have to remove the air conditioner from the window to

gain access to the controls. On other models, you should be able to gain access by

removing the screws that secure the control panel to the air conditioner frame. Next,

tilt the control panel away from the air conditioner, making sure not to pull any of

the wires off the controls.

5. Test the thermostat. To test the thermostat, disconnect the wires from the thermostat

terminals. On two-wire thermostats, remove the wires from the control, label them,

and place the ohmmeter probes on the terminals (Figure 29-6). Set the range scale on

R × 1, and test for continuity. With the thermostat set in the warmest (off) position,

you should not read continuity. When the thermostat is set to the coldest (highest)

position, you should read continuity. Inspect the capillary tube for any damage. If

the thermostat capillary tube has lost its charge, the air conditioner will not function

properly. For thermostats with more than two terminals (heat models) on the control,

you must refer to the wiring diagram on the technical data sheet for the correct

terminals to test (Figures 29-7, 29-8, 29-9, 29-10, 29-11, 29-12, 29-13, and 29-14). If the

thermostat is good, the problem must be elsewhere.

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6. Remove the thermostat. With the thermostat exposed and the wires already removed,

the capillary tube must now be removed from the evaporator coil. The capillary tube

is held in place on the coil with clips. Remove the capillary tube from the clips. If the

clips come off the evaporator coil, remember where the clips go back. The placement

of the clips is crucial for the air conditioner to function properly. Now remove the

screws that secure the thermostat body to the control panel.

7. Install a new thermostat. To install the new thermostat, just reverse the order of

disassembly, and reassemble. Then test the thermostat. Remember to reinstall the

capillary tube in the same location from which it was removed. If you do not, the air

conditioner will not cycle properly.

Thermostat (Defrost)

The defrost thermostat is only used on heat pump models. On heat pump models with

electric heat, this control is a dual-purpose control that acts as an outdoor thermostat and a

defrost control. When the thermostat sensing bulb, attached to the condenser coil, senses

enough icing on the outdoor coil, it will shut off the compressor and turn on the electric

heating element until the outdoor coil temperature reaches above 43 degrees Fahrenheit;

then the electric heater will turn off and the air conditioner will resume in the reverse cycle

mode (heat). When the outdoor coil temperature drops below 20 degrees Fahrenheit, the air

conditioner will operate in electric heat mode continuously until the outdoor coil

temperature rises above 43 degrees Fahrenheit. The fan motor will not turn off when defrost

occurs, and the reversing four-way valve will not reverse. On models without electric heat,

(a) (b)

FIGURE 29-6 (a) Testing the thermostat. (b) Bimetal defrost thermostat.

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the reversing four-way valve will reverse until the ice has defrosted. Some models use a

bimetal type of thermostat, which initiates the defrost cycle.

The typical complaints associated with failure of the defrost thermostat (heat pump

5. Test the defrost thermostat. To test the defrost thermostat, disconnect the wires

from the defrost thermostat terminals or from the selector control switch, label

them, and place the ohmmeter probes on the terminals (see Figure 29-6a). Set the

range scale on R × 1, and test the thermostat for continuity. Refer to the technical

data sheet for the model you are servicing for the position of the switch contacts

(open or closed position in the heat cycle) so that you can get the correct ohmmeter

reading. Inspect the capillary tube for any damage. If the thermostat capillary tube

has lost its charge, the air conditioner will not function properly. For defrost

thermostats with more than two terminals on the control, you must refer to the

wiring diagram on the technical data sheet for the correct terminals to test

(see Figures 29-7, 29-8, 29-9, 29-10, 29-11, 29-12, 29-13, and 29-14). If the defrost

thermostat is good, the problem must be elsewhere.

6. Remove the thermostat. With the thermostat exposed and the wires already removed,

the capillary tube must now be removed from the condenser coil. The capillary tube

is held in place on the coil with clips. Remove the capillary tube from the clips. If the

clips come off the condenser coil, remember where the clips go back. The placement

of the clips is crucial for the air conditioner to function properly. Now remove the

screws that secure the thermostat body to the control panel. If you are servicing a

model that has a bimetal clamp-on defrost thermostat (see Figure 29-6b), remove

the clamp that secures the thermostat to the condenser coil. Remember where the

thermostat was secured.

7. Install a new thermostat. To install the new defrost thermostat, just reverse the

order of disassembly, and reassemble. Then test the defrost thermostat by running

the heat cycle. Just remember to reinstall the capillary tube or bimetal clamp in the

same location from which it was removed. If you do not, the air conditioner will not

cycle properly.

Capacitor

A capacitor is a device that stores electricity to provide an electrical boost for motor starting.

Most high-torque motors need a capacitor connected in series with the start winding circuit

to produce the desired rotation under a heavy starting load. Some manufacturers will also

add a run capacitor in the circuit for motor efficiency.

The typical complaints associated with failure of the capacitor are:

• Fuse is blown or the circuit breaker trips.

• Fan motor will not run.

• Fan motor has a burning smell.

• Motor tries to start and then shuts off on overload.

To handle these problems, perform the following steps:

1. Verify the complaint. Verify the complaint by operating the air conditioner. Listen

carefully, and you will hear if there are any unusual noises or if the circuit breaker

trips. If you smell something burning, immediately turn off the air conditioner, and

pull out the plug. It will be helpful if you can locate the actual service manual for

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the air conditioner model you are working on to properly diagnose the air

conditioner.

2. Check for external factors. You must check for external factors not associated with

the air conditioner. Is the air conditioner installed properly? Does it have the correct

voltage? The voltage at the wall receptacle must be within ±10 percent of the

voltage rating on the model and serial data plate. Do you have the correct polarity?

(See Chapter 6.)

3. Disconnect the electricity. Before working on the air conditioner, disconnect the

electricity. This can be done by pulling the plug from the electrical outlet. Be sure

that you only remove the air conditioner plug. Or disconnect the electricity at the

fuse panel or at the circuit breaker panel. Turn off the electricity.

4. Gain access to the capacitor. Some models have the capacitor mounted on the fan

motor; on other models, it is mounted behind the electrical controls. Remove the

front grille and filter. Some units have either a one-piece or a two-piece grille with

locking tabs and/or screws (see Figure 29-5). Be careful not to break the tabs on the

grille. On window models, you might have to remove the air conditioner from the

window to gain access to the controls. On other models, you should be able to gain

access by removing the screws that secure the control panel to the air conditioner

frame. Next, tilt the control panel away from the air conditioner, making sure not to

pull any of the wires off the controls.

5. Test the capacitor. Many capacitors are internally fused. If you are not sure, you can

use a 20,000 ohm 2-watt resistor to discharge the capacitor. Do not use a screwdriver

to short out the capacitor. By doing so, you will blow out the fuse in the capacitor

and the capacitor will not work. Safely use an insulated pair of pliers to remove the

wires from the capacitor and place the resistor across the capacitor terminals. When

checking a dual capacitor with a capacitor analyzer or ohmmeter, you must test

both sides of the capacitor. Set the ohmmeter on the highest scale, and then place

one probe on one terminal and the other probe on the other terminal (Figure 29-15).

Observe the meter action. While the capacitor is charging, the ohmmeter will read

nearly zero ohms for a short period of time. Then the ohmmeter reading will slowly

return toward infinity. If the ohmmeter reading deflects to zero and does not return

to infinity, the capacitor is shorted and should be replaced. If the ohmmeter reading

remains at infinity and does not dip toward zero, the capacitor is open and should

be replaced.

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To test for a grounded capacitor, leave one meter probe on the capacitor terminal, and

attach the other probe to the outer casing of the capacitor or air conditioner chassis

ground. There should be no reading if the capacitor is not grounded. Next, remove

the probe from the capacitor terminal, and place the probe on the other terminal.

Again, there should be no reading indicated if the capacitor is not grounded.3

When using a capacitor analyzer to test capacitors, it will show whether the

capacitor is “open” or “shorted.” It will tell whether the capacitor is within its

microfarads rating, and it will show whether the capacitor is operating at the proper

power-factor percentage. The instrument will automatically discharge the capacitor

when the test switch is released.

6. Remove the capacitor. Remove the capacitor from its mounting bracket.

7. Install a new capacitor. To install the new capacitor, just reverse the disassembly

procedure, and reassemble.

NOT E A capacitor is rated by its working voltage (WV or WVac) and by its storage capacity in

microfarads (μF). Always replace a capacitor with one that has the same voltage rating and the

same (or up to 10 percent greater) microfarad rating.

Fan Motor

Most air conditioner models use a single fan motor with a double shaft for the fan blade and

blower wheel. There are some models that use two fan motors, powered by AC or DC volts.

Review the wiring diagram to see what type of motor(s) you are dealing with.

The typical complaints associated with failure of the fan motor are:

• No air is blowing out of the discharge grille.

• There is no cooling or heating.

• When the motor runs, there are loud noises.

• The fuse or circuit breaker trips when the air conditioner is started.

To handle these problems, perform the following steps:

1. Verify the complaint. Verify the complaint by operating the air conditioner. Listen

carefully, and you will hear if there are any unusual noises or if the circuit breaker

FIGURE 29-15

Testing a capacitor

for an open or

short circuit.

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trips. It will be helpful if you can locate the actual service manual for the air

conditioner model you are working on to properly diagnose the air conditioner.

2. Check for external factors. You must check for external factors not associated with

the air conditioner. Is the air conditioner installed properly? Does it have the correct

voltage? The voltage at the wall receptacle must be within ±10 percent of the

voltage rating on the model and serial data plate. Do you have the correct polarity?

(See Chapter 6.)

3. Disconnect the electricity. Before working on the air conditioner, disconnect the

electricity. This can be done by pulling the plug out of the wall receptacle. Be sure

that you only remove the air conditioner plug. Or disconnect the electricity at the

fuse panel or at the circuit breaker panel. Turn off the electricity.

4. Gain access to the fan motor. Before you begin to remove the fan motor, test the

motor windings. Remove the front grille and filter. Some units have either a onepiece

or a two-piece grille with locking tabs and/or screws (see Figure 29-5). Be

careful not to break the tabs on the grille. On window models, you might have to

remove the air conditioner from the window to gain access to the controls. On other

models, you should be able to gain access by removing the screws that secure the

control panel to the air conditioner frame. Next, tilt the control panel away from the

air conditioner, making sure not to pull any of the wires off the controls.

WARNING Do not touch the wiring or capacitor until it is discharged. A capacitor will hold

a charge indefinitely, even when it is not currently in use. A charged capacitor is extremely

dangerous. Discharge all capacitors immediately any time that work is being conducted in their

vicinity. Redischarge after repowering the equipment if further work must be done. Many

capacitors are internally fused. If you are not sure, you can use a 20,000 ohm 2-watt resistor to

discharge the capacitor. Do not use a screwdriver to short out the capacitor. By doing so, you will

blow out the fuse in the capacitor and the capacitor will not work. Safely use an insulated pair of

pliers to remove the wires from the capacitor and place the resistor across the capacitor terminals.

When checking a dual capacitor with a capacitor analyzer or ohmmeter, you must test both sides

of the capacitor.

5. Disconnect the motor wire leads. Disconnect the motor wire leads from the selector

switch, and label them. Check the motor windings for continuity (Figure 29-16).

Check for resistance from the common wire lead (white) to the high-speed (black)

wire lead (Figure 29-16a). Then check the resistance from the common wire lead

(white) to the medium-speed (blue) and the common wire lead (white) to the lowspeed

(red) winding (Figures 29-16b and 29-16c). If the fan motor has a capacitor

wire (brown), check for resistance from the brown wire lead to the common wire

lead (white).4 To check for a grounded winding in the motor, take the ohmmeter

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probes and check from each motor wire lead to the motor housing (Figure 29-17).

The ohmmeter will indicate continuity if the windings are grounded.

Finally, spin the motor shaft—it should turn freely. If the shaft is hard to turn, replace

the fan motor. Now move the motor shaft in an up-and-down motion perpendicular

to the motor body. The shaft should have virtually no movement. If there is a lot of

play in the end bell bearings, replace the fan motor.5

6. Remove the fan motor. To remove the fan motor, the air conditioner will have to be

uninstalled or the chassis slid out of the outer case and placed on a solid table or

workbench.

WARNING This procedure will require two people to uninstall and move the air conditioner.

(a)

White

Blue

Red

Black

White

Brown

Wire coding

identification

Black - high speed

Blue - medium speed

Red - low speed

White - common

Brown - capacitor

White

Blue

Red

Black

White

Brown

(b)

White

Blue

Red

Black

White

Brown

(c)

FIGURE 29-16 (a) Check from the common winding to the high-speed winding. (b) Check from the common

winding to the medium-speed winding. (c) Check from the common winding to the low-speed winding.

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Depending on which model you are servicing, the removal of the fan motor will

vary from manufacturer to manufacturer. However, the basic steps are the same for

every air conditioner: The fan motor is secured to the bulkhead (Figure 29-18). In

order to remove it, you must first remove the condenser fan blade. To gain access to

the fan blade, remove the screws and brackets6 that secure the condenser coil to the

fan shroud. On some models, the upper housing has a cover—remove it. The

condenser coil will have to be lifted up out of the base pan and gently moved out of

the way to gain access to the fan blade. You only have to move the condenser coil

enough to gain access to the fan blade and to provide room to remove the fan blade

without damaging the condenser coil.

WARNING When moving the condenser coil away from the fan blade, do not kink or break the

copper tubing. Remember that there is high-pressure refrigerant in the lines.

Remove the setscrew or clamp from the condenser fan blade. When removing the

fan blade, be careful not bend or damage it. To gain access to the evaporator blower

wheel (see Figure 29-18), remove the screws from the evaporator blower housing,

exposing the blower wheel. Depending on which model you are servicing, you may

have to remove part of the housing to gain access. Next, remove the clamp from the

blower wheel. You will not be able to remove the blower wheel at this time until the

fan motor is removed from the bulkhead. With the condenser fan blade removed

and the evaporator blower wheel loose on the motor shaft, you are now ready to

remove the motor. Remove the fan motor wiring from the control area, making sure

Blue

Red

Black

White

Brown

Wire coding

identification

Black - high speed

Blue - medium speed

Red - low speed

White - common

Brown - capacitor

Ohmmeter

FIGURE 29-17

Checking for a

grounded motor.

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to free up the fan motor wiring harness that may be secured to the chassis. Now

remove the fan motor nuts or bolts that secure the fan motor to the bulkhead. Grab

hold of the fan motor, and pull it out of the air conditioner while removing the

evaporator blower wheel from the motor shaft. The blower wheel will remain in the

evaporator blower housing.

1. Condenser fan blade with clamp or set screw

2. Condenser fan housing seal

3. Condenser coil and condenser fan blade housing

4. Condenser fan housing seal

5. Fan motor

6. Fan motor mounting nuts

3 2

6 4

7. Bulkhead housing

8. Screws

9. Evaporator blower wheel

10. Blower wheel clamp

11. Evaporator blower housing

12. Evaporator blower housing

FIGURE 29-18 An exploded view of the fan motor, condenser fan blade, blower wheel, and the housings.

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NOT E Replace the fan motor with a duplicate of the original for easier installation. With the fan

motor removed from the unit, it is the perfect time to chemically clean the remainder of the air

conditioner. Everything will be exposed, and it will be easier to clean the unit.

7. Reinstall the fan motor. To reinstall the fan motor, just reverse the instructions in

step 6, and reassemble. When you reinstall the condenser fan blade, make sure to

place it back on the motor shaft in the same position. Most room air conditioner

condenser fan blades have a slinger ring that is attached to the paddles. The slinger

ring will sit in a sump area in the base pan, allowing the fan blade to pick up the

condensate water, flinging it against the condenser coil. Before reinstalling the outer

cabinet or installing the air conditioner in the wall, test the air conditioner first.

Make sure the fan blade and the blower wheel are not hitting against anything.

Compressor and Overload Protector

The compressor (reciprocating or rotary type) is the heart of the vapor compression

refrigeration system. It is used to circulate the refrigerant throughout the sealed system.

The overload is attached to the compressor housing and protects the compressor.

The typical complaints associated with failure of the compressor are:

• The air conditioner will not cool.

• The room temperature is warm.

• The air conditioner does not run at all.

• The compressor makes a humming or buzzing noise and stops.

• The circuit breaker trips when the air conditioner starts up.

To handle these problems, perform the following steps:

1. Verify the complaint. Verify the complaint by asking the customer to describe what

the air conditioner is doing. It will be helpful if you can locate the actual service

manual for the air conditioner model you are working on to properly diagnose the

air conditioner.

2. Check for external factors. You must check for external factors not associated with

the air conditioner. Is the air conditioner installed properly? Does it have the correct

voltage? Check for a voltage drop during air conditioner startup. The voltage at the

wall receptacle must be within ±10 percent of the voltage rating on the model and

serial data plate. Do you have the correct polarity? (See Chapter 6.)

3. Disconnect the electricity. Before working on the air conditioner, disconnect the

electricity. This can be done by pulling the plug from the receptacle. Or disconnect

the electricity at the fuse panel or at the circuit breaker panel. Turn off the electricity.

WARNING Before you begin to service any high-voltage components within the air conditioner, you

must discharge the high-voltage capacitors first.

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WARNING A capacitor will hold a charge indefinitely, even when it is not currently in use. A charged

capacitor is extremely dangerous. Discharge all capacitors immediately any time that work is

being conducted in their vicinity. Redischarge after repowering the equipment if further work

must be done. Many capacitors are internally fused. If you are not sure, you can use a 20,000 ohm

2-watt resistor to discharge the capacitor. Do not use a screwdriver to short out the capacitor. By

doing so, you will blow out the fuse in the capacitor and the capacitor will not work. Safely use

an insulated pair of pliers to remove the wires from the capacitor and place the resistor across the

capacitor terminals. When checking a dual capacitor with a capacitor analyzer or ohmmeter, you

must test both sides of the capacitor.

WARNING Some diagnostic tests will require you to test the components with the power turned on.

When you disassemble the control panel or remove the outer cabinet, you can position the panel

in such a way that the wiring will not make contact with metal. This will allow you to test the

components without electrical mishaps.

4. Gain access to the compressor. To access the compressor, pull the air conditioner

out and away from the window or wall. Remove the outer cabinet (on some models).

This will expose the compressor, fan motor, and electrical controls (Figure 29-19 ).

Next, remove the compressor terminal cover (Figure 29-20) by removing the

retaining nut or clip that secures the cover. Remove the terminal cover and washer.

5. Test the overload protector. To test the overload protector, remove the wires from

the overload and compressor terminals. Next, place the probes of the ohmmeter on

the overload terminals (see Figure 29-20). Set the meter scale on R × 1. The reading

will show continuity. If not, replace the overload protector.

6. Test the compressor. The compressor terminals are marked C, S, and R: C indicates

the common winding terminal, S indicates the start winding terminal, and

Fan motor

and blade

Compressor

Condenser

Base pan

Service cord

Control panel

Evaporator

FIGURE 29-19 An illustration of the component location on a slide-out chassis wall air conditioner.

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R indicates the run winding terminal. Refer to the wiring diagram for the model that

you are servicing. Set the meter scale on R × 1, touch the probes together, and adjust

the needle setting to indicate a zero reading. Next, place the probes of the ohmmeter

on the terminals marked S and R (see Figure 25-37a). The meter reading will show

continuity. Now place the meter probes on the terminals marked C and S. The meter

reading will show continuity. Finally, place the meter probes on the terminals

marked C and R. The meter reading will show continuity. The total number of ohms

measured between S and R is equal to the sum of C to S plus C to R. The compressor

should be tested for proper resistance, as indicated on the wiring diagram.

Terminal cover nut and washer

Compressor

terminal cover

Terminal

cover gasket

Overload protector

Compressor

Compressor terminals

FIGURE 29-20

An exploded view of

a rotary compressor,

overload protector,

and terminal cover.

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To test the compressor for ground, place one probe on a compressor terminal, and attach

the other probe to the compressor housing or to any good ground (see Figure 25-37b). Set

the meter scale to R × 1000. The meter reading will show no continuity. Repeat this for the

remaining two terminals. The meter reading will show no continuity. If you get a continuity

reading from any of these terminals to ground, the compressor is grounded. Replace it.

WARNING This procedure may require two people to uninstall and move the air conditioner.

Electric Heater Element

Air conditioner heating elements are made with a nickel-chromium wire, having both tensile

strength and high resistance to current flow. The resistance and voltage can be measured

with a multimeter to verify if the element is functioning properly. Some manufacturers are

also using calrod heaters instead of nickel-chromium wire heaters. This type of heater can be

tested for resistance and voltage, too.

The typical complaint associated with failure of the electric heater element is that the air

conditioner will not heat at all. To handle this problem, perform the following steps:

1. Verify the complaint. Verify the complaint by checking the control setting. Turn the

control to the highest setting for heat; then turn it back to a normal setting to see if

the air conditioner starts heating. It will be helpful if you can locate the actual

service manual for the air conditioner model you are working on to properly

diagnose the air conditioner.

2. Check for external factors. You must check for external factors not associated with

the air conditioner. Is the air conditioner installed properly? Is the exhaust or fresh

air intake vent open? Check for the correct voltage to the air conditioner. The

voltage at the wall receptacle must be within ±10 percent of the voltage rating on

the model and serial data plate. Do you have the correct polarity? (See Chapter 6.)

Explain to the user how to set the controls.

3. Disconnect the electricity. Before working on the air conditioner, disconnect the

electricity to the unit. This can be done by pulling the plug from the receptacle. Or

disconnect the electricity at the fuse panel or at the circuit breaker panel. Turn off

the electricity.

4. Gain access to the electric heater element circuitry. To access the electric heater

element circuitry, remove the front grille and filter. Some units have either a onepiece

or a two-piece grill with locking tabs and/or screws (see Figure 29-5). Be

careful not to break the tabs on the grill. On window models, you might have to

remove the air conditioner from the window to gain access to the controls. On other

models, you should be able to gain access by removing the screws that secure the

control panel to the air conditioner frame. Next, tilt the control panel away from the

air conditioner, making sure not to pull any of the wires off the controls.

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5. Test the electric heater element. At this point, you do not have to disassemble the air

conditioner to determine if the electric heater element is defective. Locate the wiring

diagram (see Figure 29-8), and trace the electric heater element circuit. You will notice

that the heater element, thermal fuse, and heater limit control (thermostat) are wired

in series with the selector switch and operating thermostat. These five components

make up the heating circuit. Locate the electric heater element wiring, and disconnect

the wires from the terminals. For example, in the wiring diagram shown in Figure 29-8,

the orange and red wires from the electric heater element go to the capacitor common

terminal and to the number 4 terminal on the selector switch. If you remove those two

wires from their terminals, you have just isolated the electric heater element, thermal

fuse, and the heater limit control. Set your ohmmeter to the R × 1 scale, and check for

continuity between those two wires.7 If the ohmmeter reads resistance in the circuit,

then the problem is elsewhere. If your ohmmeter reads an open circuit, you will have

to remove the electric heater assembly for further testing.

6. Remove the electric heater assembly. The electric heater assembly is located in the

evaporator blower housing on the discharge side. It may be behind a metal screen on

older models. For newer models, the heater element is located behind the evaporator

coil. To remove the heater assembly, the air conditioner will have to be uninstalled.

WARNING This procedure may require two people to uninstall and move the air conditioner.

Remove the screws that secure the top panel on the evaporator blower housing (see

Figure 29-18). On some models, part of the evaporator housing can be removed for

easy access to the heater assembly. Once you gain access to the heater assembly,

remove the screws that secure the assembly to the air conditioner. Replace with a

duplicate of the original.

NOT E With the electric heater assembly removed from the unit, it is the perfect time to chemically

clean the remainder of the air conditioner. Everything will be exposed, and it will be easier to

clean the unit. Just remember to protect the electrical components and fan motor.

7. Install the heater assembly. To install a new electric heater assembly, just reverse

the disassembly procedure, and reassemble. Reinstall all panels and the front grille,

and restore the electricity to the air conditioner. Test the room air conditioner heat

operation.

1116 P a r t V I : A p p l i a n c e S e r v i c e , I n s t a l l a t i o n , a n d P r e v e n t i v e M a i n t e n a n c e P r o c e d u r e s

Reversing Valve Solenoid Coil

A reversing valve solenoid is a device used to convert electrical energy into mechanical

energy. When the solenoid is energized, it acts like an electromagnet and is positioned to

move a predesignated metal object within the reversing valve.

The typical complaint associated with failure of the reversing valve solenoid coil is that

the air conditioner will not heat. To handle this problem, perform the following steps: