6–3
T-349
Will not initiate defrost
manually
Manual defrost switch defective
Replace
Defrost temperature sensor open
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 (COOLING)
High discharge pressure
Condenser coil dirty
Condenser fan rotating backwards
Condenser fan inoperative
Refrigerant overcharge or noncondensibles
Discharge pressure regulator valve defective
Discharge service valve partially closed
Open
Suction modulation valve malfunction
Low suction pressure
Suction service valve partially closed
Open
Filter-drier partially plugged
Low refrigerant charge
Expansion valve defective
No evaporator air flow or restricted air flow
Excessive frost on evaporator coil
Evaporator fan(s) rotating backwards
Discharge pressure regulator valve defective
Suction modulation valve malfunction
Suction and discharge
pressures tend to equalize
when unit is operating
Heat exchanger defective
Replace
Compressor valves defective
Compressor cycling/stopped
Check
6.8
ABNORMAL NOISE OR VIBRATIONS
Compressor
Loose mounting bolts
Tighten
Worn bearings
Worn or broken valves
Liquid slugging
Insufficient oil
Condenser or Evaporator Fan
Bent, loose or striking venturi
Check
Worn motor bearings
Bent motor shaft
CONDITION
POSSIBLE CAUSE
REMEDY/
REFERENCE
SECTION
Summary of Contents for 69NT40-541-306
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