Why compressors fail part 6

They include broken evaporator fan belts, bad fan motors, dirty coils, and dirty filters. A dirty condenser coil or a failed condenser fan motor allows heat to build in the coil rather than being rejected into the atmosphere.

The compressor then has to pump against excessive pressure, which may cause it to overheat, resulting in accelerated component wear, damage, or complete failure. One method of minimizing refrigerant accumulation in the compressor, or a flooded start, is to incorporate a pump down control system. In this system a solenoid valve can be installed in the liquid line. The compressor pumps down the system and a low-pressure switch stops the compressor after the refrigerant has been removed from the low side of the system.

The compressor restarts, after a time delay, when the thermostat energizes the solenoid valve again. Both voltage and current anomalies cause an increase in temperature, which may go unnoticed for a long period of time. There are several things that can be done to help prevent repeat compressor failures, such as: improving equipment maintenance and record keeping; using proper start-up procedures; improving systems and diagnostic skills; and inspecting the failed compressors.

A proper diagnosis as to the cause of the failure is also essential. As mentioned previously, compressors are designed to handle normal thermal temperature gain. However, when they are operated outside their design conditions, careful attention has to be taken to avoid reduced life expectancy and potential damage.

Cost-effective operation and maintenance require implementing new technology, installing electronic protective devices to monitor and to warn about the repeated tripping of the compressor. At this point the liquid in the sump oil literally explodes out of the oil causing the crankcase to fi ll with refrigerant foam and oil droplets. The system is in the off cycle, however, during this period refrigerant has migrated to the compressor and mixed with the oil.

Note the pressure gauge. This vapour will increase rapidly in its volume and prevent oil reaching the furthest bearings and con rods away from the oil pick up point. These bearings quickly run dry and overheat. Sometimes on smaller machines the main front or motor end bearing will seize and stall the motor.

On larger machines the powerful motor often continues to spin the crankshaft and then the upper most con rods seize onto the crankshaft and as the crankshaft continues to 2 Lit.

Liquid fl ash off has washed the lubrication from the bearings, in this case we can see where the con rod has seized to the bearings by welding of aluminium from the con rod to the bearing surface. In smaller compressors this type of seizure will most likely stall the motor. Due to the fl ash off of liquid refrigerant washing lubrication from the bearings when seizure of the con rod on the crankshaft occurs the motor continues to spin breaking the con rod.

The broken con rod often smash into the piston causing further damage. These metallic particles can be thrown around inside the machine and can damage the motor insulation and cause a spot burn or total motor burn out. Flooded starts can often be simply diagnosed by high oil levels seen in the oil level sight glass, and during the start up mode the oil is seen to foam sometimes for only a few seconds, sometimes for a few minutes.

The longer the foaming lasts, the more wear and damage is taking place. Engineers can easily diagnose these signs of Flood back problems, but the compressor failures can often be mistaken for Liquid Flood back or Flooded Starts as the failed components often look very similar under inspection.

This mixture is partially Non-Compressible and often causes the suction valves to break, which can lead to broken piston crowns and damaged discharge valves and head gaskets. The mixture of oil and liquid is partially non-compressible and results in broken and pitted discharge valves and even broken piston crowns. This also applies to products already on order provided that such alterations can be made without subsequent changes being necessary in specifi cations already agreed.

E-mail glenn. Short-link Link Embed. Share from cover. Share from page:. More magazines by this user. The cold room may be frozen or chilled, but it will normally be colder than the compressor. So lets see what happens now. The compressor starts up via the thermostat, solenoid valve and then the LP switch. The compressor runs OK. When the compressor is subjected to one of the above problem scenarios, where the amps drawn rises, or the compressor temperature rises.

The compressor will get to a point where it Here we have a Klixon tted to a 3-phase motor. The Klixon is the compressors last line of defence and should not be used to cycle the compressor. The Klixon is not in the compressors safety circuit as its in the.

Therefore, the thermostat is still calling for duty ie contacts closed, the solenoid valve is still energised and open, and the Low Pressure switch is still made calling for the compressor to run. However, the compressor cant run due to it being stopped on its internal Klixon. So the liquid refrigerant continues to pour uncontrolled into the cold evaporator.

The refrigerant vapour slowly migrates back into the compressor slowly diluting the compressors lubricant. Depending on how hot the compressor motor has become, will have a bearing on the time that the compressor is OFF on its Klixon. This can be as long as 8 Hours. When the Klixon does eventually reset, the compressor restarts and either the lubricant is so heavily diluted with refrigerant that the bearings are washed out and they seize, or the liquid simply oods back into the compressor causing suction and discharge valves to break and pistons and con rods to break and most likely smash the compressor.

Seized bearings, broken pistons and con rods even completely smashed compressors are all possible outcomes when the compressor is cycling on the Klixon because no overload protector has been tted.

If an overload had been tted and wired through the control circuit, providing the overload had been set to the correct setting so that any over current that the compressor initiated would cause the overload to trip, thereby stopping the compressor and also breaking the feed to the solenoid coil and forcing it to close.

The compressor motor would have been saved from running in an overloaded state, which weakens the motor insulation and reduces the compressors life time, and the solenoid valve forced to shut preventing liquid refrigerant lling the evaporator and causing fatal damage to an innocent machine.

The cold room temperature alarm would give the plant operator chance to check the plant and rectify the problem, as against having to replace a costly compressor simply because of a dirty condenser or a faulty defrost control. NOTE:- The liquid line solenoid valve must always be closed, if the compressor is stopped by one of its safety controls.

The compressors Klixon is the last line of safety, when all else fails. The moral of this story is Penny wise, Pound Foolish. Danfoss can accept no responsibility for possible errors in catalogues, brochures and other printed material. Danfoss reserves the right to alter its products without notice. This also applies to products already on order provided that such alterations can be made without subsequent changes being necessary in specications already agreed.

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