Appendix N: Troubleshooting
Table N1: VHC-36, -42 and -50 Troubleshooting
Problem
Cause
Solutions
Unit will not turn on.
Occupancy contact open.
Check external wiring.
Unoccupied recirc contact open.
Check the wiring in the control panel.
Unit will not turn off.
Occupancy contact closed.
Check the external wiring.
Unoccupied recirc contact closed.
Check the wiring on the control panel.
Air from supply diffusers too cold.
Imbalance of supply and exhaust air.
Check filters and heat exchanger for blockage.
Check balance of airflows.
Install post-heat module.
Unit makes an annoying noise.
Blower wheel out of alignment.
Remove the motor/blower assembly.
Adjust blower wheel.
Enthalpy wheel wiper seal not
functioning properly.
Check for proper seal operation.
Enthalpy wheel freezing.
Imbalance of supply and exhaust air.
Check filters and heat exchanger for blockage.
Check balance of airflows.
Defrost damper not functioning.
Check for operation of damper actuator.
Pre-heater not functioning.
Check for operation of damper actuator.
Enthalpy wheel not running.
Unit is in free cooling.
Check jumper wire for proper operation.
Unit is in recirc defrost.
Check unit circuit breaker.
Drive motor capacitor failure.
Check motor electrical connections.
Drive motor failure.
Check capacitor connections. Check motor operation with
a new capacitor.
Drive motor relay in control box.
Check relay wiring.
Drive belt.
Check for drive belt derailment off drive pulley or failure.
Drive pulley.
Check for securely fastened pulley on motor shaft.
Motor and blower not functioning.
Electrical supply interrupted.
Check unit circuit breaker.
Fan motor capacitor.
Check motor electrical connections.
Fan motor failure.
Check capacitor connections.
Fan motor contactor failure.
Check contactor wiring. Check contactor operation.
Fan drive belt.
Check for a tripped overload relay.
Fan drive pulleys.
Check for securely fastened pulley(s) on motor or fan
shaft(s). Set screw setting at 100 in-lbs to 130 in-lbs.
Only supply fan will turn on.
Unit is in recirc defrost (recirc units).
Wait until unit is out of defrost.
Unit is in unoccupied recirc (recirc
units).
Check external wiring.
Damper end switch not made.
Check outdoor air damper for proper wiring.
Check that the end switch is making.
Only exhaust fan will turn on.
Unit is in defrost (exhaust units).
Check connection to motor.
Motor wiring incorrect.
Damper end switch not made.
Check exhaust air damper for proper wiring.
Damper will not open.
Electrical supply interrupted.
Check wiring on damper actuator.
Defrost relay in control box.
Check relay wiring. Check relay operation.
Damper opens when it should be
closed.
Wires are reversed.
Reverse wires #2 and #3 on damper actuator.
Compressor will not turn.
No power.
Ensure main disconnect is on and measure main terminal
block for voltage.
Wiring is incorrect.
Verify if compressor is wired correctly.
Controlled temperature lower (cooling)
or higher (heating) than thermostat
setting.
Adjust thermostat setting.
Compressor failed.
Replace compressor.
VCES-VHC-IOM-1F – VHC-36, -42 & -50
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