Unit Will Not Terminate Heating; Unit Will Not Defrost Properly; Abnormal Pressures - Carrier 69NT40-561-399 Operation And Service Manual

6.5

UNIT WILL NOT TERMINATE HEATING

Condition
Unit fails to stop heating
6.6

UNIT WILL NOT DEFROST PROPERLY

Condition
Will not initiate defrost automati-
cally
Will not initiate defrost manually
Initiates but relay (DR) drops out
Initiates but does not defrost
6.7

ABNORMAL PRESSURES

Condition
High discharge pressure
Possible Cause
Controller improperly set
Controller malfunction
Heater termination thermostat remains closed along with
the heat relay
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
Keypad is defective
Defrost temperature sensor open
Low Line Voltage
Heater contactor or coil defective
Heater(s) burned out
Possible Cause
Condenser coil dirty
Condenser fan rotating backwards
Condenser fan inoperative
Refrigerant overcharge or non-condensibles
Discharge service valve partially closed
Electronic expansion valve (EEV) control malfunction
6–3
Remedy/Refer-
ence Section
Reset
Section 6.9
Section 7.13
Remedy/Refer-
ence Section
Section Table 4–
3
Tighten
Replace
Replace
Replace
Replace
Replace
Section 3.3
Replace
Section 7.13
Remedy/Refer-
ence Section
Section 7.10.1
Section 7.10
Section 7.11
Section 7.3
Open
Replace
T-365