Unit Will Not Defrost Properly; Abnormal Pressures (Cooling) - Carrier 69NT40-541-505 Operation And Service Manual

6.6

UNIT WILL NOT DEFROST PROPERLY

Condition
Will not initiate defrost
automatically
Will not initiate defrost manually
Initiates but relay (DR) drops out
Initiates but does not defrost
Frequent defrost
6.7

ABNORMAL PRESSURES (COOLING)

Condition
High discharge pressure
Low suction pressure
Suction and discharge pressures
tend to equalize when unit is
operating
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Possible Cause
Defrost timer malfunction (Cd27)
Loose terminal connections
Defective wiring
Defrost temperature sensor defective or heat termination
thermostat open
Heater contactor or coil defective
Manual defrost switch defective
Defrost temperature sensor open
Low line voltage
Heater contactor or coil defective
Heater(s) burned out
Wet load
Possible Cause
Condenser coil dirty
Condenser fan rotating backwards
Condenser fan inoperative
Refrigerant overcharge or noncondensibles
Discharge service valve partially closed
Suction modulation valve malfunction
Suction service valve partially closed
Filter-drier partially plugged
Low refrigerant charge
Expansion valve defective
No evaporator air flow or restricted air flow
Excessive frost on evaporator coil
Suction modulation valve malfunction
Heat exchanger defective
Compressor valves defective
Compressor cycling/stopped
search engine
6–3
Remedy/Refer-
ence Section
Table 4–5
Tighten
Replace
Replace
Replace
Replace
7.21
3.3
Replace
7.13
Normal
Remedy/Refer-
ence Section
7.10.1
7.11
7.11
7.7.1
Open
7.17
Open
7.12
7.7.1
7.16
7.13
6.6
7.17
Replace
7.8
Check
T-368