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Dehumidifiers Repair

area. Humidity is defined as the amount of water vapor in the air and is measured

in terms of relative humidity (RH %). The higher the RH percentage, the more water

vapor in the air. The optimum relative humidity level in an area is generally considered to be

between 30 percent and 50 percent. Humidity levels exceeding 50 percent with temperatures

over 70 degrees Fahrenheit can be uncomfortable, unhealthy, and in most cases cause personal

property damage. Anything above this range may promote bacteria growth or mold. In colder

climates, during the heating season, humidity levels should be maintained between 30 percent

and 40 percent to prevent moisture from collecting or condensing on the windows and doors.

Dehumidifiers (Figure 30-1) were designed to remove unwanted moisture from the air in

a given area.

Sizing a Dehumidifier

Dehumidifiers, when properly set, can maintain the desired humidity level in that area.

The capacity is usually measured in pints per 24 hours and is determined by two factors: the

square footage of the space that needs to be dehumidified and the conditions that exist in

the space before dehumidification. Table 30-1 depicts a dehumidifier sizing chart.

Another measure that can determine the size of dehumidifier the consumer needs is the

amount of air the appliance can move over a certain period of time. Dehumidifiers measure

this in cubic feet per minute (CFM). The CFM is an important measure for dehumidification

because the unit can only extract moisture from the air that passes through the dehumidifier.

All of the air in a room must flow through the dehumidifier in order to remove moisture.

To calculate the CFM you need from the dehumidifier, multiply the cubic feet of the area by

the recommended air changes per hour (ACH) in Table 30-1, and then divide that number

by 60 minutes. The resulting number is the CFM the dehumidifier should have.

Principals of Operation

A refrigeration system (Figure 30-2) is used to collect the moisture from the air. The dehumidifier

may have either a reciprocating (split phase) or a rotary (permanent split capacitor) compressor

that circulates the refrigerant in the dehumidifier. The evaporator operating temperatures

are around 33 to 37 degrees Fahrenheit. When moisture-ladened air passes over the

1135

CHAPTER

FIGURE 30-1

A typical portable

dehumidiier.

Condition Without

Dehumidification

500

Sq. Ft.

1,000

Sq. Ft.

1,500

Sq. Ft.

2,000

Sq. Ft.

2,500

Sq. Ft.

3,000

Sq. Ft.

In humid weather, the area is

moderately damp and it has

a musty odor. (60–70% RH)

ACH=3

10 pints 14 pints 18 pints 22 pints 26 pints 30 pints

In very damp areas, it always

feels damp and spots appear

on the walls and floors.

(70–80% RH) ACH=4

12 pints 17 pints 22 pints 27 pints 32 pints 37 pints

In areas that are very wet,

the walls and the floor are

sweating or there is seepage.

(80–90% RH) ACH=5

14 pints 20 pints 26 pints 32 pints 38 pints 44 pints

In areas that are extremely

wet; wet floor, laundry room,

high-load conditions.

(90–100% RH) ACH=6

16 pints 23 pints 30 pints 37 pints 44 pints 51 pints

The higher the humidity in an area, the more often the air should cycle through the dehumidifier. This is known as

Air Changes per Hour, or ACH.

PART VI

evaporator, the moisture will collect on the evaporator coil and condense into a liquid. The

cool air is then drawn through the condenser coil and warms the air before it is recirculated

back into the room area. The water collected on the evaporator coil will run off the coil into

a bucket. Many dehumidifier models include a built-in in humidistat, a device that allows

the consumer to set the humidity level desired for that room. Once the room reaches the

desired humidity level, the dehumidifier will cycle on and off automatically to maintain

that RH level.

Safety First

to install, maintain, or repair any dehumidifiers. 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 dehumidifier, please call

your service manager.

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.

Dehumidifiers in General

Much of the troubleshooting information in this chapter covers dehumidifiers 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 a particular brand’s

reliability.

FIGURE 30-2

A typical refrigeration

system used in a

dehumidiier. The air

is drawn in through

the evaporator and

expelled out through

the contender coil

by a fan.

Suction tube

Discharge tube

Capillary tube

Collected water

Air

low

(out)

Air

low

(in)

Condenser

Fan

Evaporator

Location and Installation of a Dehumidifier

When installing the dehumidifier in the home, you must allow 12 inches of space on all sides

of the dehumidifier so that air can circulate properly (see Figure 30-3). The dehumidifier can

be installed on the floor, table, or shelf. When installing the dehumidifier on a table or shelf,

make sure the table or shelf can support the weight of the dehumidifier, including the weight

of the bucket full of water. Next, plug the dehumidifier into a 120 volt properly grounded

Dehumidifier Maintenance

The dehumidifier’s coils should be chemically cleaned at least annually to remove the dirt

and slime buildup within the unit. Clean the outer case and cabinet (Figure 30-4a) with a

soft cloth and a mild detergent. Next, vacuum the grille, or use a brush on the grill. Do not

use abrasives or bleach on the dehumidifier. About once a month, remove the water bucket

and clean it to avoid growth of mold, mildew, and bacteria. Don’t forget to wash the air

filter and shake off the excess water and let it air dry, and then reinstall it (Figures 30-4b and c)

at least once a month also.

Step-by-Step Troubleshooting by Symptom Diagnosis

When servicing a dehumidifier, 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

dehumidifier. 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 dehumidifier, and then correct the problem.

12''

12''

FIGURE 30-3

Place the dehumidiier

within 12 inches of

any walls or other

blockages that might

prevent proper air

circulation.

PART VI

Dehumidifier Will Not Run (No Fan, No Compressor)

control setting.

Condenser Fan Motor Runs (Compressor Not Running)

Condenser Fan Motor Does Not Run (Compressor Is Running)

Condenser Fan Motor and Compressor Running (Evaporator Coil Frozen Up)

higher than 65 degrees Fahrenheit. Frost should disappear within 60 minutes. If not,

check the sealed system.

ilter (c).

(a) (b) (c)

Condenser Fan Motor and Compressor Running (No Dehumidification)

Dehumidifier Is Running (Insufficient Dehumidification)

Dehumidifier Runs Continuously

Repair Procedures

Each repair procedure is a complete inspection and repair process for a single dehumidifier

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

Electronic Components

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

The typical complaints associated with the electronic components are:

To prevent electrostatic discharge (ESD) from damaging expensive electronic

components, follow the steps in Chapter 11.

To handle these problems, perform the following steps:

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

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

PART VI

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

dehumidifier model you are working on to properly diagnose the dehumidifier. The

service manual will assist you in properly placing the dehumidifier in the service

test mode for testing the dehumidifier functions.

the dehumidifier. Is there electricity to the dehumidifier? 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?

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.

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

(Figures 30-5a, b, c, and d). Next, tilt the control panel away from the dehumidifier,

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

check the different functions of the dehumidifier. 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.

screws that secure the printed circuit board to the dehumidifier console frame.

Disconnect the connectors from the electronic control board and display.

Top cover

screws

Rear of

dehumidiier

(a) (b)

(d)

(e) (f)

Front

screws

Float actuator

Front grille

screws

Rear of

dehumidiier

(c)

as shown.

PART VI

procedure and reassemble. Reinstall all panels and the front grille and bucket.

Then, restore the electricity to the dehumidifier. Test the dehumidifier operation.

To prevent ESD from damaging expensive electronic components, simply follow the

steps in Chapter 11.

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. The capacitor can also be used

for motor efficiency.

The typical complaints associated with failure of the capacitor are:

To handle these problems, perform the following steps:

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 dehumidifier and

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

the dehumidifier model you are working on to properly diagnose the dehumidifier.

the dehumidifier. Is the dehumidifier 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.)

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

sure that you only remove the dehumidifier plug. Or disconnect the electricity at

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

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 Figures 30-5 and 30-6). On other models, you should

be able to gain access by removing the screws that secure the control panel to the

dehumidifier frame.

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.

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 dehumidifier

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.

FIGURE 30-6

A typical dehumidiier

without its panels

attached.

Condenser

fan motor

Control

panel

Compressor

Run capacitor

Evaporator and

condenser coils

PART VI

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.

procedure and reassemble.

Fan Motor

Dehumidifiers use a single fan motor with a single shaft for the fan blade or blower wheel.

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

To handle these problems, perform the following steps:

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

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

dehumidifier model you are working on to properly diagnose the dehumidifier.

the dehumidifier. Is the dehumidifier 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.)

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

sure that you only remove the dehumidifier plug. Or disconnect the electricity at

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

the motor windings. Remove the outer wrapper and the front grille and filter

(Figures 30-5 and 30-6).

panel, and label them. Check the motor windings for continuity (Figure 30-6). Using

the wiring diagram, check for resistance on the condenser fan motor windings. To

check for a grounded winding in the motor, take the ohmmeter probes and check

from each motor wire lead to the motor housing. 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.

that hold the fan motor bracket in place. Then, remove the fan blade or blower wheel.

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 dehumidifier.

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. Before reinstalling the outer

cabinet on the dehumidifier, test the dehumidifier first. Make sure the fan blade or

the blower wheel is not hitting against anything.

Compressor and Overload Protector

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

It is used to circulate the refrigerant throughout the sealed system. The overload is attached

to the compressor housing. The overload protects the compressor. Some models are equipped

with a relay to assist the compressor in starting.

PART VI

The typical complaints associated with failure of the compressor are:

To handle these problems, perform the following steps:

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

manual for the dehumidifier model you are working on to properly diagnose the

dehumidifier.

the dehumidifier. Is the dehumidifier installed properly? Does it have the correct

voltage? Check for a voltage drop during dehumidifier 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.)

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.

(Figures 30-5 and 30-6). This will expose the compressor, fan motor, and electrical

controls (Figure 30-6). 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.

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

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

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

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

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.

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

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.

Bucket Switch

The bucket switch is a single-pole, double-throw (SPDT) device that shuts off the dehumidifier

when the bucket is full of water. The switch is mounted to the frame directly behind the bucket

(Figure 30-7). The switch is activated by the float assembly.

The typical complaints associated with failure of the bucket switch are:

Float

(a)

Bucket

switch

(b)

FIGURE 30-7

Do not run the

dehumidiier without

the bucket. (a) The

loat assembly. (b) The

loat switch in the rear

of the dehumidiier.

PART VI

To handle these problems, perform the following steps:

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

manual for the dehumidifier model you are working on to properly diagnose the

dehumidifier.

the dehumidifier. Is the dehumidifier installed properly? Does it have the correct

voltage? Check for a voltage drop during dehumidifier 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.)

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.

releasing the actuator from the float assembly (Figures 30-5a and b). Remove the outer

wrapper to gain access to the bucket switch (Figure 30-6). To remove the float assembly,

pull the pin (Figure 30-8), and remove the float assembly. To remove the bucket

switch assembly (Figure 30-9a), squeeze the tabs to remove the bucket switch.

terminals on the switch. Figure 30-9b shows testing between common and normally

open terminals. In the switch rest position, there will be maximum resistance. From

common to the normally closed terminal, there should be zero resistance. When the

bucket switch lever is depressed, common to the normally open terminals, there

should be zero resistance. From the common to the normally closed terminals, you

should have a reading of maximum resistance.

component, just reverse the disassembly procedure

and reassemble. Reinstall all panels and the front

grille and bucket. Then, restore the electricity to the

dehumidifier. Test the dehumidifier operation. To

prevent ESD from damaging expensive electronic

components, simply follow the steps in Chapter 11.

Defrost Thermostat

The defrost thermostat is mounted on the suction line

(Figure 30-10).

The typical complaints associated with failure of the

defrost thermostat (heat pump models only) are:

To handle these problems, perform the following steps:

control to the highest setting for heat, and then turn it back to a normal setting to

see if the dehumidifier starts heating. It will be helpful if you can locate the actual

service manual for the dehumidifier model you are working on to properly

diagnose the dehumidifier.

the dehumidifier. Is the dehumidifier installed properly? 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.)

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.

Pin

loat assembly.

Normally

open

Normally

closed Common

ohmmeter to test the switch contacts.

(a) (c)

PART VI

outer wrapper and the front grille and filter (Figures 30-5 and 30-6). Next, tilt the

control panel away from the dehumidifier, making sure not to pull any of the wires

off the controls. The manufacturer placed the defrost thermostat control on the

suction line (Figure 30-10). The defrost thermostat is a nonadjustable thermostat

without a stem or knob attached to it. On other models, the defrost thermostat

might be a bimetal thermostat that is clamped to the end of the evaporator coil with

two wires coming out of it that lead back to the control panel.

FIGURE 30-10

Defrost thermostat

attached to the

suction line. When the

evaporator goes below

37 degrees

Fahrenheit, the defrost

thermostat opens,

shutting off the

compressor. The

condenser fan motor

will continue to run.

When the suction

line temperature

rises to 59 degrees

Fahrenheit, the defrost

thermostat closes

and the compressor

starts up.

Suction line to

compressor

Defrost

thermostat

thermostat, disconnect the wires from the

defrost thermostat terminals on the control

panel, label them, and place the ohmmeter

probes on the terminals (see Figure 29-6b). Set

for continuity. If the temperature is above

60 degrees Fahrenheit, the resistance reading

will be zero, indicating that the contacts are

closed. Now, place the thermostat in a bucket of

ice. With the ohmmeter leads still attached, the

contacts should open when the temperature

drops below 37 degrees Fahrenheit.

exposed and the wires already removed, the

defrost thermostat must now be removed from

the suction line. The thermostat is held in place

on the suction line with a spring load clamp (Figure 30-11). Remove the thermostat

clamp. If the clamp comes off the suction line, remember where the clamp goes

back. The placement of the clamp and thermostat is crucial for the dehumidifier to

function properly.

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

the dehumidifier. Just remember to reinstall the bimetal clamp in the same location

from which it was removed. If you do not, the dehumidifier will not cycle properly.

Wiring Diagrams and Schematics

The wiring diagrams and schematics that are used in this chapter might be helpful to

diagnose a dehumidifier (see Figures 30-12, 30-13, 30-14, 30-15, and 30-16). These diagrams

are not a substitution for the exact wiring schematic that might be on the inside cover of the

outer wrapper.

Endnote

1. When the bearings wear out in the end bell of the