CPR Industries - Air Compressor Parts & Repair
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Compressor failure mode, symptoms and corrections

A handy reference for analysis of a failed compressor, to aid in finding cause of failure and take corrective action. Replacement new or remanufactured compressors fail at four times the rate of original compressors indicating replacement failures are caused by system problems

Liquid slugging

Broken reeds, rods, or crankshaft. Loose or broken discharge bolts. Blown gaskets. 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. Slugging is a result of refrigerant migration into the oil on the off cycle.
Correction:
1. Check pump down cycle operation.
2. Is TXV sized and operating properly?
3. Suction line sized properly?
4. Check unloading.

Liquid washout

Worn pistons and/or rings. Cylinders worn. Scored pins. Scored and/or broken rods. Worn bearings. Scored crankshaft. This is a result of refrigerant washing oil off surfaces. Off cycle migration of saturated refrigerant into crankcase. Compressor starts up resulting in a mass of foam which when pumped washes bearing surfaces of oil film necessary for proper lubrication. Washout is a minor condition of slugging.
Correction:
1. Check TXV bulb and super heat setting.
2. Is TXV oversized?
3. Check to be sure the crankcase heater is on during the off cycle.

Liquid dilution

Rotor drag. Worn bearings. Scored and/or broken rods. Scored crankshaft. 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 bearings will occur.
Correction:
1. Check TAY bulb.
2. Check superheat setting.
3. Check defrost cycle.

High discharge temperature

Discolored 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. This is a result of temperatures in the compressor head and cylinders becoming too hot that the oil loses its ability to lubricate.
Correction:
1. High compression rotation: check for low suction and high discharge pressures. Low load and evaporator problems.
2. Check low pressure control setting.
3. Check for dirty condenser, inoperative condenser fan and ambient temperature.
4. Check air flow across compressor.

Lack of lubrication

Scored bearing. Broken rods. Scored crankshaft. Low oil in crankcase. This is a result of lack of enough oil in crankcase to properly lubricate the running gear.
Correction:
1. Check oil failure switch.
2. Check pipe sizing and also for oil traps.
3. Inadequate defrost.
4. Low load.
5. Eliminate short cycling.

Electrical

Many motors fail as a result of a mechanical or lubrication failure. Many fail due to malfunctioning external elecrical components.

General or uniforms burn

Entire winding is uniformly overheated or burned.
Correction:
1. Check for low voltage.
2. Rapid cycling of compressor.
3. Loose terminal connection.
4. Unbalance voltage.

Single phase burn

Two phases of a three phase motor are overheated or burned. A result of not having current through the unburned phase and overloading the other two phases.
Correction:
1. Check contacts in starter and contact slide mechanism for binding.
2. Terminal connections on compressor.
3. Unbalanced voltage.
4. Blown fuses.

Half winding single phase burn

Two phases as when one half of the motor has a single phasing condition on a part wind motor with a two contactor system.
Correction:
1. Check both contactors as one will be defective.
2. Check timer for proper time delay.

Start winding burn

Only the start winding is burned in a single phase motor due to excessive current flowing through the start winding.
Correction:
1. Check C, S, and R, wiring.
2. Starting capacitor and/or start relay.
3. Compressor overloaded.

Run winding burn

Only the run winding is burned in a single phase motor.
Correction:
1. Check relay.
2. Check run capacitors.

Primary single phase burn

This will show as only one phase burned. Other two will be OK. A result of losing one phase in the primary of a X to Y or Y to X transformer.
correction:
1. Check transformer for proper voltage incoming and outgoing.

Trouble

Possible cause

Corrective measure

High condensing pressure

Air or non-condensable gas in system.

Insufficient water or air flowing through condenser.

Evaporative condenser clogged or limed.

Too much liquid in receiver, condenser tubes submerged in liquid refrigerant.

Purge air from condenser

Increase quantity of water or air

Clean condenser water tubes.

Draw off liquid into service cylinder.

Low condensing pressure

Too much water or air flowing through condenser.

Condensing water too cold

Liquid refrigerant flooding back from evaporator.

Leaky compressor discharge valve(s)

Reduce quantity of water or air.

Check expansion device adjustment, examine fastening of thermal expansion valve bulb(s)

Remove heads, examine valves.  Replace any found defective.

High suction pressure

Overfeeding of expansion device

Leaky suction or discharge valves

Malfunction of compressor capacity control system

Excess load

Regulate expansion valve, check bulb attachment and superheat adjustment

Remove head, examine valves and replace if worn

Check capacity control system

Reduce load to normal

Low suction pressure

Restricted liquid line, or suction strainer screens

Insufficient refrigerant in system

Too much oil in system

Improper adjustment of expansion valve(s) or liquid control device(s)

Expansion valve power element dead or weak

Pump down, remove restriction, examine and clean screens

Check for refrigerant shortage

Remove oil

Adjust device(s) for proper superheat - approximately 10'F

Replace expansion valve or power element

Compressor will not run

Electric power cut off

Fuses blown

Overload devices tripped

Low voltage

Trouble in starting switch or control circuit

Seized compressor

Check power supply

Test fuses and renew if necessary

Check overload devices and find cause of overload

Check voltage

Close switch manually to test power supply.  If ok, check control circuit including temperature and pressure controls and capacity control device.

Repair or rebuild compressor

Compressor runs continuously with insufficient reduction of load temperatures.

Shortage of refrigerant

Individual cylinders not loading

Incorrect control switch settings

Repair leak and recharge system

Check and correct pumping ability of individual cylinders - replace suction and/or discharge valves and parts as needed

Check and correct capacity control system

Reset control switches or replace

Compressor short cycles or stops on high pressure cutout.

Presence of air or foul gas

Insufficient water or air flowing through condenser, clogged condenser

Purge condenser

Check water or air flow. Check for scaled or fouled tubes in water cooled condenser. In evaporative type, check for fouled surfaces and insufficient air or spray water

In air cooled type, check for fouled surfaces, or lack of air flow

Compressor stop on oil failure switch

Plugged oil strainer

Excessive liquid repair in pump

Clean air strainer

Pump down observe level

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