Aprilaire 1750A - Troubleshooting

TROUBLESHOOTING
TABLE 7 – Green LED Codes
Activity Status
Solid ON Compressor ON
Blinking 1 sec. ON & 1 sec. OFF Sampling
Blinking 1/2 sec. ON & 1/2 sec. OFF Defrosting
Alternating Green & Red Control knob was left in Test Mode
Technical Support is available Monday through Friday, 7:00 a.m. to 5:00 p.m. CST, at (800) 334-6011. Use the guides on the following pages to
identify and correct system faults. Contact Technical Support before replacing the unit or components and for additional troubleshooting.
LED CODES
The dehumidifier control board uses the Status LED to communicate
current status or a fault code. Faults can be either critical or non-
critical. In either case, when a fault is detected, the red LED will flash
the fault code and all outputs will immediately turn off. A critical
fault can be cleared by repairing the fault and cycling power to the
dehumidifier. A non-critical fault will be cleared when the fault is
repaired. Cycling power is not required.
TABLE 8 – Red LED Codes
Number
of Blinks
Fault Type Failure Mode Failure Condition Action
1 Non-Critical Internal RH
sensor fault.
RH sensor open or shorted. 1. Check connection between sensor board and control board.
2. If connection okay, replace sensor board, Part No. 4752.
2 Critical Internal
temperature
sensor fault.
Temperature sensor open or shorted. 1. Check connection between sensor board and control board.
2. If connection okay, replace sensor board, Part No. 4752.
3 Non-Critical Model 76
Remote Control
fault.
Model 76 Remote Control not
communicating with dehumidifier.
1. Check connections between Model 76 and dehumidifier
control board.
2. If connections are correct and secure, turn off the
dehumidifier and remove the Model 76. Use a short section
of 4-wire cable to reconnect the Model 76 to the control
board. Turn the dehumidifier back on and increase the
dryness level setting on the Model 76. If the dehumidifier
turns on, the problem is with the wiring between the
dehumidifier and control.
3. If the dehumidifier does not turn on, call Technical Support.
4 Critical Insufficient
capacity.
After 20 minutes of compressor operation,
the frost sensor temperature is not at least
5°F below the inlet air temperature.
1. Check the frost sensor connection at the control board.
2. Remove the side panel (when facing side of unit, on/off
switch will be on left) and verify the temperature sensor is
not damaged, is fully inserted in the sensor well, and the
well is filled with thermal paste.
3. If the sensor is not damaged and positioned correctly,
contact Technical Support.
5 Non-Critical Inlet air
temperature out
of range.
Internal temperature sensor reads out
of 50°F –105°F range for compressor
operation. NOTE: If compressor is on when
fault condition occurs, the compressor will
turn off. If the compressor is not on when
the fault condition occurs, there is no fault.
1. Circulate air through the unit by setting the Cycle Period to
1 hour and Cycle Time to 60 minutes. After a minimum of
10 minutes, cycle power to the dehumidifier.
2. If fault persists, call Technical Support.
6 Critical Frost sensor
failure.
Frost temperature sensor open or shorted. 1. Check the frost sensor connection at the control board.
2. Remove the side panel (when facing side of unit, on/off
switch will be on left) and verify the temperature sensor is
not damaged, is fully inserted in the sensor well, and the
well is filled with thermal paste.
3. If the fault persists, contact Technical Support.
7 Non-Critical Float switch
open.
Open circuit between float switch inputs. 1. Empty the condensate pan.
2. Check the float switch connection at the control board.
3. If not using float switch, verify jumper is between float
switch terminals on dehumidifier control board.
4. If the problem persists, replace the float switch.
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