COMPRESSOR MAINTENANCE

The long service life is of course what is desired for the compressors. Today, the compressors are designed for trouble-free operation, long service life and in many cases; they are operated on 24 hours in 365 days of the year. Still, such operation regime is not as difficult at all as in cyclic operation, where the compressors are subject to variable temperatures and oil cannot be maintained at stable viscosity.

The compressors should be designed to cope with liquid overflow, excessive discharge pressure and periodic abnormalities, in addition to the requirements for regular operation. The compressor manufacturers design and manufacture the compressors that capable of resisting additional difficulties of the industry, which is praiseworthy, but no manufacturer has ever sold a complete system. At this point, professional cooling technician takes the stage, since majority of compressor failure are attributed to the system deficiencies, rather than the wear or tear. The technical expertise, skill and common sense in installing and operating the system will determine the real service life of the system in general and compressor in particular. The technician may draw attention to the deficiencies and serious problems, if not make the selection.

Several factors and reasons adversely affect the compressor’s efficiency, service life and abnormal operation.

LOSS OF EFFICIENCY
The loss of efficiency may be due to several reasons.

• If the refrigerant enters into the compressor, the efficiency and thus the capacity will adversely be affected. Besides, the refrigerant overflow may lead to the physical damage and loss of capacity.

• Leaking pressure relief valves will reduce the pumping efficiency and rapid increase in the crankcase pressure.

• Leaking suction valves seriously affect the compressor’s efficiency in particular the low temperature applications.

• Loose pistons may cause excessive refrigerant leakage and deficiency in pumping effectiveness.

• Loose connecting rods and piston pins due to worn bearings prevent upward travel of the piston at he compression stroke. This will end up with increase in the gap volume and excessive expansion.

• Slip of the belt on the pulley groove in belt drives gives rise to loss of efficiency.

EXCESSIVE LOADING OF MOTOR
Unsatisfactory operation of the compressor may now and then indicate the motor loading problem. Abnormally high or low motor loading is an indicator of irregular operation of the compressor.

• Loose pistons lead to the mechanical problems like insufficient operation of the suction valve or excessive gap volume. They all give rise to decease in motor loading.

• Another frequently encountered problem is plugging of the suction chamber or entry filter (due to system dirt). As a result, the actual pressure in the cylinders drops rapidly and becomes much less than the pressure indicated by the suction side pressure gauge. In such case, the motor load will extremely decrease.

• The motor will be overloaded unless the discharge valve operates properly or partially clogged (resulting pressure increase will not be indicated by the pressure gauge) and pistons operate smoothly.

• The motor will be overloaded if the suction temperature is excessive as a result of excessive loading or any other reasons.

• Excessive condensing attributed to the condenser problem will result in excessive temperature increases and thus overloading of the motor.

• The voltage drop at the compressor will yield to overloading of the motor, in combination with other operational problems, let alone efficiency loss in power supply or feed loss.

TURBULENT OPERATION
This is mostly indication to a problem in the system. There might be abnormal situation anywhere in the system or a broken part in the compressor that impedes normal operation. It is clear that the replacement of the compressor will not eliminate the problem, if the problem is anywhere in the system. It is therefore following possible reasons must be checked, before replacing the compressor;

• Overflow: Be sure that only superheated gas enters into the compressor.

• Excessive oil: In most cases, oil is stuck in the evaporator or on the suction line and intermittently drawn into the compressor in fragments.

• Loose belt: Improper belt may give rise the noise in belt and pulley drive units.

• Improper compressor installation: Due to improper installation, the pads of the hermetic type compressor my hit to the supports and force the compressor foundation.

NOISY COMPRESSOR OPERATIONS
The noise during compressor operation may be attributable to any one of following reasons:

• Improper lubrication: The lubrication oil may be insufficient for proper lubrication of the bearings. If the system is complete with the oil pump, it might be improper or out of order. The foreign materials may clog the oil inlet or outlet ports and the system may run out of the proper oil supply.

• Excessive oil: The increased quantity oil in the system might be the reason for improper distribution or overflow in the system.

• Piston or bearing seizure: The piston or bearing seizure may give rise to metallic noise at the pistons or bearings. The compressor may generate similar noises while it is operated for some time, even if the piston or bearing allowances are normal. The noise generated at the pistons and bearings in the system during operation after a while might be due to “copper coating” a phenomenon attributed to the moisture in the system.

• Loose parts in the compressor: The spring loaded parts in the compressor may come loose and hit the internal wall of the compressor.

• Loose bearings: Loose connecting rod, piston pin or crankshaft bearings will naturally give rise to abnormal noises. The noise and premature wear are likely for the compressor where the crankshaft and bearing are not installed on the same axis and offset to each other or with respect to the compressor wall.

• Broken valves: A broken part of the suction or discharge valve may come loose at the compressor top and give rise to noise at every stroke. The residues of the foreign materials like chips, slag, etc. on top of the piston head will cause to the generation of noise.

• Loose rotor or crankpin. A loose rotor on the shaft of the hermetic compressors due to the loose key may lead to noise in the operation of the compressor. If the crankshaft and crankpin is not rigid or a loose locking device might be the reason of the generating the knocks in operation.

• Vibration of discharge valves: The vibration of the lamella or disk of the discharge valve during operation might give rise to the natural noise generation at the compression stroke in particular for the compressors operating at low suction pressure. This may not give a maloperation of the compressor; however, the compressor manufacturer might be requested for a modification.

• Refrigerant detonation: This might be observed in the evaporator, condenser or suction line under certain conditions. It might be heard as a knock and/or whistling sound from the suction line or discharge pipe. This is in fact not a mechanical knocking but the slight impacts heard during the suction or compression strokes that combines with such factors like the size and length of the cooling lines, number of elbows and similar other dimensional factors.