Ultimate Fix-It-Yourself Manual: Large appliances--Dehumidifiers

A dehumidifier is essentially a scaled-down air conditioner that doesn’t cool. It has the same basic components as an air conditioner—compressor, fan, and coils—and uses a standard refrigeration cycle. An adjustable humidistat turns on the fan and compressor when the moisture in the air reaches the point set on the humidistat. The fan draws in moist room air and pushes it across cold evaporator coils. As water condenses on the coils, it’s collected in a water container. Unlike an air conditioner’s con denser, which expels heat outdoors, a dehumidifier’s built-in condenser coils return the heat to the room.

Dehumidifier problems sometimes stem from extremes of humidity. A unit may run continuously when the air is very moist or not start at all when it’s very dry. Because a dehumidifier closely resembles an air conditioner, many air-conditioner repairs can be adapted to a dehumidifier.

Full indicator light; Humidistat; Condenser coils, Filter vaporator; Fan blade; fan motor mounting nut; Back panel; Water container; leads; Deicer; switch; Compressor; Drain tray; Overflow switch; Compressor start relay and overload protector. Note: Details of repair and disassembly may vary, depending on appliance model, If your dehumidifier differs markedly from this one, see Appliance repair basics.

Gaining access:

To access components in back of dehumidifier, unplug unit, then unscrew or unsnap back panel and remove it. Unscrew controls or switches attached to cabinet if you can reach them. If not, access them from the front.

To open front of unit, take out water container and filter; then snap out grille and remove it. Take out screws securing cabinet to base and drain tray; then remove drain tray, and lift off the cabinet.

= = = USE AND CARE = = =

Vacuum the evaporator coils every 6 to 12 months, using a brush attachment. Be careful not to damage the coils’ fins. Remove grime or mildew with a mild household cleanser and an old toothbrush, or use an auto degreaser that’s safe for use on aluminum. Spray with water to rinse off all of the degreaser.

Empty the water container daily, or more often on humid days when water collects quickly. Don’t let water stagnate in the container. Once a month, clean the container with a sponge and mild detergent and let it dry completely.

Wash or replace the a filter once a month as you would on an air conditioner.

Oil the tan motor if it requires lubrication. Check your owner’s manual, or look for oil ports on the motor. Oil as recommended each season; a fan motor typically requires only 1 or 2 drops of SAE 20 oil in each port.

= = = =

Fan and compressor:

To check these parts, unplug the unit and open the cabinet. Without touching any wires, plug in and turn on the unit. If the fan doesn’t run, unplug the unit, disconnect the fan motor leads, and probe them with a VOM on RX1. Look for a reading between 25 and 75 ohms; if it’s infinity, replace the motor. To do this, remove the fan blade , then the motor mounting nuts or screws. If the fan does run, feel the compressor for vibration. If there is none, check the deicer, the start relay, and the overload protector , which is mounted on the start relay and is removed by pulling the relay off the compressor pins. If these parts test OK, the compressor has likely failed.

Testing the compressor start relay:

1. Remove leads and set VOM on RX1. First test coil by probing terminals at both ends of coil. Look for a reading of zero or very low ohms. 2. Pull relay off compressor pins. Probe run terminal and start terminal; look for infinity reading. Invert relay and repeat test; look for zero ohms reading.

Humidistat, overflow switch, and deicer:

A humidistat senses the air’s moisture and turns the dehumidifier on or off at the set point. Test it when the humidity is low. If there’s a separate on-off switch, test it too. An overflow switch shuts off the unit before the water container spills. On some models, this switch is activated by a float; on others, it has a diaphragm activated by water rising in a tube, like the water-level switch on a washer. The deicer is a bimetal switch that turns off the compressor before the evaporator coils frost but lets the fan keep running. Unplug the unit before testing a switch.

Test humidistat with VOM on RX1. Remove leads, and clip probes to terminals. Turn knob; look for reading to jump from zero to infinity (or vice versa) when you hear a click. A partial or continuous reading indicates a fault (unless humidity is very low or high).

Test overflow switch with VOM on RX1. Take off leads; clip probes to COM and humidistat terminals. Look for zero ohms. Lift float (or lower tube into water on diaphragm type); look for infinity. Repeat test with COM and indicator light terminals; look for opposite results.

To test deicer, disconnect its leads and dismount it. With VOM on RX1, clip probes to leads. Look for a reading of zero. Then put deicer in a freezer for 10 mm., and test it again. Look for reading of infinity. If deicer fails either test, replace it.


  • Won’t run
  • De-humidifies poorly
  • Noisy
  • Evaporator coils frost up
  • Leaks water
  • Bad odor
  • Power off at outlet or faulty power cord
  • Faulty overflow switch or humidistat
  • Dust-clogged evaporator coils or bent fins
  • Bent, broken, or loose fan blade
  • Faulty deicer switch
  • Faulty fan motor or dry motor bearings
  • Faulty compressor start relay
  • Faulty compressor overload protector
  • Faulty compressor motor
  • Low refrigerant level (coils frost)
  • Loose screws on trim or exterior panels
  • Loose fan blade or motor mounts
  • Fan striking something
  • Tubing rubbing together or against other part
  • Air temperature too low
  • Air circulation blocked or coils clogged
  • Faulty deicer switch
  • Low refrigerant level
  • Faulty overflow switch
  • Stagnant water in base or dirty coils

See General troubleshooting.

Test and replace

Vacuum coils. Or straighten fins.

Replace or tighten.

Test and replace.

Test fan motor. Or oil bearings.

Test and replace.

Test and replace.

Test for continuity. Have serviced if needed.

Have serviced.



Remove obstruction. Gently bend tubing in place.

Don’t run unit when it’s below 65°F.

Move unit away from wall. Vacuum coils.

Test and replace

Have serviced.

Test and replace

Wipe up water; wash base. Wash coils.

[Degree of difficulty: Simple -- Average Complex • Volt-ohm meter required: ]


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