5 | P a g e
4. If the compressor does start, verify that the refrigeration system is operating sufficiently
to prevent a “4-blinks” fault.
a. If applicable, disconnect the duct from the discharge of the dehumidifier. Verify that
the flap damper on the outlet of the dehumidifier opens/closes freely.
b. Verify that there is not a lengthy amount of ductwork (more than 50 feet) attached
to the inlet side, that the ductwork is free of obstructions and kinks and that the filter
is clean – remove the filter for this test if dirty.
c. Ensure the front and back panels are in place and
assembled with screws. DO NOT REMOVE PANELS
DURING THIS TEST.
d. Remove the control door. Disconnect all electrical
connections to the HVAC equipment by removing the
HVAC Equipment terminal block from the control
board. Disconnect any remote control by removing
the REMOTE terminal block.
e. Move the LOCAL/EXTERNAL System Setup dip switch
on the control board to LOCAL (if the switch is labeled
A/B, no need to change the position)
f. Adjust the control knob to the highest setting – 7 (do
not put the unit in TEST mode as this will allow the
compressor run for only one minute) to initiate a
dehumidifier call.
g. Before the compressor starts, measure the DC voltage
across the frost sensor terminals on the control
board. Do not disconnect the wires from the terminals when reading the voltage.
The voltage represents a temperature and should be near the temperature of the
incoming air. The voltage should start to increase as the coil gets colder.
h. Measure the voltage again after 10 minutes of compressor run time to determine if it
has increased. The voltage should increase to indicate a temperature drop of ten
Frost Sensor
Voltage (DC)
Frost Sensor
Temperature (°F)
Frost Sensor
Voltage (DC)
Frost Sensor
Temperature (°F)
Top Dip Switch is
Local/External
HVAC Equipment
Terminal Block
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