Fan does not run with
Compressor runs briefly
but cycles on & off with
humidity control turned to
Evaporator coil frosted
continuously, low de-
Unit not providing
Unit removes some
water, but not as much as
Unit Test to determine
If the refrigerant charge is lost due to service or a leak, a new charge must be accurately weighed in. If any
of the old charge is left in the system, it must be recovered before weighing in the new charge. Refer to the
unit nameplate for the correct charge weight and refrigerant type.
This compressor is equipped with a two terminal external overload and a run capacitor, but no start
capacitor or relay.
Recommended Troubleshooting steps
1. Loose connection in fan circuit.
2. Obstruction prevents fan rotation.
3. Defective fan.
4. Defective fan relay.
5. Defective fan capacitor.
1. Defrost thermostat loose or defective.
2. Low refrigerant charge.
3. Dirty air filter(s) or airflow restricted.
1. Check control wire connections (check connections at fresh air damper
2. Defective fresh air damper.
3. Dirty air intake. Clean outside intake hood.
1. Air temperature and/or humidity have dropped.
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 leaks.
8. Defective compressor.
9. Restrictive ducting.
10. Optional Condensate Pump Safety Switch open.
1. Detach field control wiring connections from main unit.
2. Connect the R and FAN contacts from the main unit together; only the
impeller fan should run. Disconnect the wires.
3. Connect the R and DHUM contacts 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 problems next.
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 disconnected!
6. Turn on the humidity control. The compressor and impeller fan should
7. If these tests work, the problem is most likely in the field control wiring.
TrueDry DR90 Dehumidification System