DH90 Dehumidifier • For HVAC Installer Only
Fan runs when there is a call for dehumidifica-
tion and the ventilation control is OFF, but the
compressor cycles on and off too frequently.
1. Low ambient temperature and/or humidity
causing unit to cycle through defrost mode.
2. Defective compressor overload.
3. Defective compressor.
4. Defrost thermostat defective.
5. Dirty air filter(s) or airflow restricted.
6. Low refrigerant charge, causing defrost
control to cycle.
7. Bad connection in compressor circuit.
Fan does not run with fan switch in either
Fan does not run with ventilation activated.
Compressor runs briefly but cycles on & off
with humidity control turned to ON.
1. Loose connection in fan circuit.
2. Obstruction prevents fan rotation.
3. Defective fan.
4. Defective fan relay.
5. Defective fan capacitor.
Evaporator coil frosted continuously, low de-
1. Defrost thermostat loose or defective.
2. Low refrigerant charge.
3. Dirty air filter(s) or airflow restricted.
Unit not providing ventilation.
1. Check control wire connections (check
connections at fresh air damper also).
2. Defective fresh air damper.
3. Dirty air intake. Clean outside intake hood.
Unit removes some water, but not as much as
1. Air temperature and/or humidity have
2. Humidity meter and or thermometer used
are out of calibration.
3. Unit has entered defrost cycle.
4. Air filter dirty.
5. Defective defrost thermostat.
6. Low refrigerant charge.
7. Air leak such as loose cover or ducting
8. Defective compressor.
9. Restrictive ducting.
10. Optional Condensate Pump Safety Switch
Unit Test to determine problem:
1. Detach field control wiring connections
from main unit.
2. Connect the yellow and green pigtails
from the main unit together; only the
impeller fan should run. Disconnect the
3. Connect the yellow and blue pigtails from
the main unit together; the compressor
and impeller fan should run.
4. If these tests work, the main unit is
working properly. You should check the
control panel and field control wiring for
5. Remove the control panel from the
mounting box and detach it from the
field installed control wiring. Connect the
blue, yellow, and green wires from the
control panel directly to the corresponding
colored pigtails on the main unit.
Leave the violet, white, and red wires
6. Turn on the fan switch; the impeller fan
should run. Turn off the fan switch.
7. Turn on the humidity control; the
compressor and impeller fan should run.
8. If these tests work, the problem is most
likely in the field control wiring.