Semi-hermetic Compressor Troubleshooting Guide

The compressor maintenance processing 


The compressor generates heat from the electrical motor, friction between different moving parts, and heat from compression. When the compressor is running outside, its operating envelope or its design conditions is when problems begin.

What can cause overheating

High discharge temperatures, High compression ratios, High superheat, Inadequate motor cooling, High return gas, Lack of external cooling Overheating occurs anytime when the oil in the compressor is heated so much that it will lose its ability to lubricate >300F/149C.

How to prevent Overheating

Always check the discharge temperature of 6″ or 150mm from the discharge service valve and make sure you stay below 225F/107C Semi-Hermetics. Other compressors like Reciprocating Hermetic, Scrolls, Rotary, and Screw will have different values so you will need to check the manufacturer manual for those numbers. For example, some Scroll you want to keep below260F/127C. If you are above 225F/107C you need to investigate why.

You want to make sure you maintain compression ratios per design. Copeland Scroll Compressor for AC has a max of 11:1 before the floating seal unloads and refrigeration Scrolls are 26:1.

Make sure you set the minimum to superheat so your return gas temperature back at the compressor is not so high that the oil starts to lose its lubrication abilities(POE – 300F/149C) or breakdown (POE – 350F/177C)

Always insulate the suction line because if it is not insulated it will pick up all the heat in the space and bring it back to the compressor.

Properly set low-pressure control so that system does not take a very long time to pump down or run the compressor outside the compressor envelope.

Make sure the Condenser is clean and there are no pressure drops in the suction line

Have the correct charge in the system so the refrigerant coming back can cool the compressor rotor and stator.

Use required cooling methods like head cooling fan, demand cooling, or liquid injection when required by the compressor manufacturer.

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