Compressor Failure Identification
Most compressors fail due to system malfunctions which must be corrected to prevent repeat failures. After a compressor fails, field examination of the failed compressor often will reveal system problems.
Liquid Slugging
Diagnosis:
Broken reeds, rods, or crankshaft.
Loose or broken discharge bolts.
Blown gaskets.
Cause:
Slugging is a result of trying to compress liquid in the cylinders.
Liquid may be either refrigerant or oil or more likely a combination of both.
Correction:
Maintain proper compressor and evaporator superheat.
Prevent uncontrolled liquid return (particularly oil) with accumulators.
Locate compressors in warm ambient or install pump to down cycle.
Correct abnormal low load conditions.
Liquid Washout
Diagnosis:
Worn rods and bearings.
Worn pistons and cylinder on lower end.
Worn crankshaft and oil pump.
Scored cover bearing and crankshaft.
Cause:
This is the result of refrigerant washing oil off wearing surfaces. Off-cycle migration of saturated refrigerant into crankcase. Compressor starts up resulting in a mass of foam which when pumped washes bearing surfaces clear of oil film necessary for proper lubrication. Severe migration results in slugging.
Correction:
Locate compressor in warm ambient or install pump down cycle.
Check crankcase heater operation.
Liquid Dilution
Diagnosis:
Rotor drag/shorted stator.
Worn bearings.
Scored and/or broken rods.
Scored crankshaft.
Worn oil pump.
Cause:
This is a result of liquid refrigerant returning to compressor during running cycle. Oil becomes diluted and lubrication for oil pump and end bearing may be adequate, but as it progresses down the crankshaft insufficient oil to lubricate the rods and main bearing will occur. This may allow the rotor to drag on the stator and short out the stator.
Correction:
Maintain proper compressor and evaporator superheat.
Prevent uncontrolled liquid return with accumulator if necessary.
Correct abnormal low load conditions.
Check of defrost cycle.
Check for oversized TXV.
High Discharge Temperature
Diagnosis:
Discoloured valve plate (Cannot rub off).
Overheated or burned valve reeds.
Worn rings and pistons.
Worn cylinders.
Scored rods, bearing and crankshaft.
Spot burn in stator.
Cause:
This is a result of temperatures in the compressor head and cylinders becoming so hot that the oil loses its ability to lubricate.
Correction:
High compression ratio: check for low suction and high discharge pressure. Low load and evaporator problems.
Check oil pressure control settings
Check for dirty condenser, inoperative condenser fan and ambient temperature.
Check air flow across compressor.
Lack of Oil
Diagnosis:
Scored bearings.
Broken rods.
Scored crankshaft.
Low oil in crankcase.
Cause:
This is a result of lack of enough oil in crankcase properly lubricate the running gear.
Correction:
Check oil failure switch operation.
Check pipe sizing and also for oil traps.
Check for inadequate defrost.
Correct abnormal low load conditions.
Eliminate short cycling.
Electrical
Cause:
Many motors will fail as a result of mechanical or lubrication failure. Many fail due to malfunctioning external electrical components.
General or Uniform Burn
Diagnosis:
Entire winding is uniformly overheated or burned
Cause:
Entire winding is uniformly overheated or burned.
Correction:
Low voltage.
Rapid cycling of compressor.
Inadequate motor cooling.
Unbalanced voltage.
Single Phase Burn
Diagnosis:
Two phases of a three phase motor are overheated or burned.
Cause:
A result of not having current through the unburned phase and overloading the other two phases.
Correction:
Replace contactor.
Check terminal connections on compressor.
Check for balanced voltage.
Check for blown fuses.
Half Winding Single Phase Burn
Diagnosis:
Half of winding burned.
Cause:
This shows as when one half of the motor has a single phasing condition on a PART WIND MOTOR with a two contactor system.
Correction:
Check both contactors as one may be defective.
Check Timer for proper time delay.
Start Winding Burn
Diagnosis:
Only start winding burned.
Cause:
Only the start winding is burned in a single phase motor due to excessive current flowing through the start winding.
Correction:
Check C, S and R wiring.
Check starting capacitor and/or start delay.
Check for compressor overloading.
Run Winding Burn
Diagnosis:
Only run winding burned.
Cause:
Only the run winding is burned in a single phase motor.
Correction:
Check relay.
Check run capacitors.
Primary Single Phase Burn
Diagnosis:
Only one phase burned.
Cause:
This will show as only one phase burned. Other two will be OK. A result of losing one phase in the primary of a Δ to Y or Y to Δ transformer.
Correction:
Check transformer for proper voltage incoming and outgoing.