What does it mean when the compressor valves are leaking?

When the compressor is run outside of design limits, the fi rst thingthat happens is that the discharge temperature/superheat increases.This increase in temperature is fi rst felt inside the cylinders and at thedischarge valves. As the temperature increases, the lubrication to thecylinder and piston is literally cooked away causing the now dryrubbing surfaces to score and fi ne iron particles are scrapped fromthe cylinder wall and end up in the compressor sump oil and aroundthe compressor motion gear. This overheated oil as it passes throughthe discharge valves causes the oil to coke or carbonise on thevalveplate causing the valve to leak bye, elevating the temperature evenhigher. This gas leaking past the valves and pistons will elevate thecompressor suction pressure and cause loss of capacity in the machine.As the oil in the compressor starts to break down due to the heat, acids andcarbon are produced. These acids will, to a certain extent, be absorbed by thedrier desiccant, but will eventually start attacking the motor windinginsulation and cause either a spot burn or full motor burn out.

A compressor’s valves may become inefficient because of valve warping from overheating or lack of lubrication, or from having carbon and/or sludge deposits on them preventing them from sealing properly. Here are a few additional reasons why such incidents occur:

• Slugging of refrigerant and/or oil;

• Moisture and heat, causing sludging problems;

• Refrigerant migration problems;

• Refrigerant flooding problems;

• Overheating the compressor, which may warp the valves;

• Acids and/or sludge in the system deteriorating parts;

• TXV set incorrectly — too little superheat, causing flooding or slugging;

• TXV set incorrectly — too much superheat, causing compressor overheating;

• Undercharge causing high superheat and compressor overheating; and

• Low load on the evaporator from a frozen coil or fan not working, causing slugging or flooding of the compressor.

when gas or refrigerant is leaking from valves