6–3
T-372
Will not initiate defrost
manually
Manual defrost switch defective
Replace
Keypad is defective
Replace
Defrost temperature sensor open
Replace
Initiates but relay (DR) drops
out
Low line voltage
Initiates but does not defrost
Heater contactor or coil defective
Replace
Heater(s) burned out
Frequent defrost
Wet load
Normal
6.7 Abnormal Pressures
High discharge pressure
Condenser coil dirty
Condenser fan rotating backwards
Condenser fan inoperative
Refrigerant overcharge or non-condensibles
Discharge service valve partially closed
Open
Electronic expansion valve (EEV) control malfunction Replace
Low suction pressure
Incorrect software and/or controller configuration
Check
Failed suction pressure transducer (SPT) or evapora
-
tor pressure transducer (EPT)
Replace
Suction service valve partially closed\
Open
Filter drier partially plugged
Low refrigerant charge
No evaporator air flow or restricted air flow
Excessive frost on evaporator coil
Evaporator fan(s) rotating backwards
EEV control malfunction
Replace
Failed digital unloader valve (DUV)
Replace
Suction and discharge
pressures tend to equalize
when unit is operating
Compressor operating in reverse
Compressor cycling/stopped
Check
Failed digital unloader valve (DUV)
Replace
6.8 Abnormal Noise or Vibrations
Compressor
Compressor start up after an extended shutdown
Normal
Brief chattering when manually shut down
Compressor operating in reverse
Loose mounting bolts or worn resilient mounts
Tighten / Replace
Loose upper mounting
Loose slugging
Condenser or Evaporator
Fan
Bent, loose or striking venturi
Check
Worn motor bearings
Bent motor shaft
Condition
Possible Cause
Remedy / Reference
Section