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Problem
Probable Cause
Solution
Compressor
Short Cycles
Thermostat location or malfunction
Check thermostat, check heat
anticipator setting
Improper refrigerant charge
Check subcooling, verify superheat
Defective high or low pressure control
Check high or low pressure switch
Cycling on internal overload
Possible tight bearings – see above
Defective expansion valve
Check TXV and superheat
Poor air distribution
Check ductwork for recirculation
High discharge pressure
See above – high discharge pressure
Leaking discharge valves in compressor
See above – high suction pressure
Running Cycle Too
Long Or Unit
Operates Continuously
Refrigerant undercharged
Check subcooling
Dirty filter or evaporator coil
Check filter, coil and airflow
Dirty or clogged condenser coil
Check coil and airflow
Air or other non-condensables in system
Check equalized high side pressure with
equivalent outdoor temperature
Defective compressor
See above – high suction pressure
Restriction in suction and liquid line
Check for restrictions in refrigerant circuit
Control contacts stuck
Check thermostat, shorts in wiring, slave
relay compressor contactor
Supply Air Temperature
Too High
Refrigerant undercharge or leak in system
Check subcooling and check for leaks
Evaporator plugged with dirt or ice
Check evaporator, airflow and filter
Improperly adjusted or defective expansion
valve
Check superheat and adjust TXV,
check bulb
Defective compressor
Check compressor for proper operation
High discharge pressure
See above- high discharge pressure
Airflow is too high
Check external static pressure
Supply Air Temperature
Too Low
Airflow is too low
Check evaporator coil, filter, check for
closed dampers, grills, drive for loose parts,
belts, misalignment, check external
static pressure
Return air temperature too low
Check entering air wet bulb conditions
Blower Motor
Not Running
Improper wiring
Check wiring diagram
Defective motor
Check motor controller
Defective thermostat or control circuit
Check “R” and “G” Circuit
Motor off on overload protector
Allow motor to cool, check amperage
Table 13.3: Refrigeration Circuit, Cont.
PR Series Installation, Operation, and Maintenance Manual
