41
Table 13 — Compressor
LEGEND
PROBLEM
POSSIBLE CAUSE
SOLUTION
Compressor will not start
Power off, loose electrical connections or fuse open
Check disconnect switch, fuses and wiring.
Compressor contactor not closing
Check voltage to contactor coil, transformer slave
relay, thermostat.
Internal compressor thermal overload open
If compressor is hot, allow 2 hours to cool – see
below.
Compressor defective
Check compressor for electrical failure. Compressor
may be seized; check for lock rotor amps.
High or low pressure switch open or defective
Check calibration of high or low pressure switch.
Oil pressure control open or defective
Check oil failure control – see below.
Compressor starts but cuts out
on
low pressure switch
Low on refrigerant
Check sight glass and check pressures.
Airflow restricted
Check for dirty evaporator coil, dirty filters, dampers
closed, iced evaporator, VFD settings, check motor
amps, duct design.
Restriction in liquid line
Check head pressure. Check and adjust TXV, if not
functioning properly. Check pressure drop across fil-
ter drier.
Defective low pressure switch
Check calibration of switch.
Compressor starts but cuts out
on
high pressure switch
Refrigerant overcharged
Check pressures, charge by subcooling.
Condenser fan control has incorrect setting
Check calibration of the low ambient control.
Fan motor defective
Check fan motor.
Condenser coil inlet obstructed or dirty
Check coil and inlet clearances and for possible air
recirculation.
Air or non-condensables in system
Compare liquid refrigerant pressure with the
saturated pressure. If the presence of air or non-
condensables is suspected, the refrigerant must be
reclaimed through a service port. The system must
then be re-evacuated to 250-500 microns and
recharged. The filter-drier should also be replaced
before charging.
Defective high pressure switch
Replace switch.
Restriction in discharge or liquid line.
Check discharge and liquid line pressures. Check
TXV.
Compressor cuts out on ther-
mal overload
Low voltage
Check incoming voltage leg-to-leg. All three legs
must be within 10% of the required voltage and the
leg-to-three-leg average voltage variation must be
less than 2% on each leg.
Sustained high discharge pressure
Check running amperage and conditions described
under high discharge pressure.
High suction and discharge pressures
Check TXV setting. Check for air in system.
Defective compressor overload
Allow compressor to cool for two hours if compressor
is hot. Recheck for open circuit.
Defective run capacitor
Check run capacitor for compressor and fan motor.
Improper refrigerant charge
Check subcooling.
Bearings or pistons too tight
Check for low oil level.
Allow time for compressor to cool
Check dome temperature of compressor.
Noisy compressor
Scroll compressors are rotation sensitive
Reverse wiring at disconnect switch may require
blower be rechecked for rotation.
Refrigerant overcharged
Check pressures and subcooling.
Excess or insufficient oil in compressor crankcase
Check oil level on hermetic compressors. Check total
equivalent feet of piping. Add oil, as recommended.
Liquid floodback
Check TXV setting. Refrigerant overcharge refriger-
ant circuit problem.
Cyclical noise pattern
Digital compressors have a significant shift in gener-
ated noise when running uploaded.
Compressor defective
Replace compressor.
TXV
—
Thermal Expansion Valve
VFD
—
Variable Frequency Drive
