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5-3
T -309
CONDITION POSSIBLE CAUSE
REMEDY/
REFERENCE
SECTION
5.6 UNIT WILL NOT DEFROST PROPERLY -- Continued
Will not initiate defrost
Manual defrost switch defective Replace
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manually
Defrost temperature sensor open 4.9.5
Initiates but relay (DR) drops
out
Low line voltage 2.3
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Heater contactor or coil defective Replace
Initiates but does not defrost
Heater(s) burned out 6.15
Frequent defrost Wet load Normal
5.7 ABNORMAL PRESSURES (COOLING)
Condenser coil dirty 6.11
Condenser fan rotating backwards 6.12
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Condenser fan inoperative 6.12
High discharge pressure
Refrigerant overcharge or noncondensibles 6.7.1
Discharge service valve partially closed Open
Suction modulation valve malfunction 6.20
Faulty suction pressure transducer Replace
Suction service valve partially closed Open
Filter-drier partially plugged 6.13
Low refrigerant charge 6.7.1
Low suction pressure
Expansion valve defective 6. 14
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No evaporator air flow or restricted air flow 6.15
Excessive frost on evaporator coil 5.6
Evaporator fan(s) rotating backwards 2.3
Suction modulation valve malfunction 6.20
Suction and discharge pressures
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Compressor operating in reverse 5.14
ten
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to equa
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en un
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operating
Compressor cycling/stopped Check
5.8 ABNORMAL NOISE OR VIBRATIONS
Compressor start up after an extended shutdown
N
o
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m
a
l
Brief chattering when manually shut down
Normal
Compressor operating in reverse 5.14
Compressor
Loose mounting bolts or worn resilient mounts Tighten/Replace
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Loose upper mounting 6.8.1 step r.
Liquid slugging 6.14
Insufficient oil 6.9
Bent, loose or striking venturi Check
Condenser or Evaporator Fan
Worn motor bearings 6. 12/6.17
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Bent motor shaft 6.12/6.17