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Contamination in refrigeration systems cause many compressor failures and this is usually from day one of the installations. The two largest contamination issues are dirt in the system causing restrictions or spot burns on the winding and moisture which can cause acid in the system. Systems with Polyolester oil (POE) are prone to have issues if the system is not evacuated properly because POE is very hygroscopic. Hygroscopic means it will absorb moisture very fast and if the system, compressor, or oil container is left open to the atmosphere especially in high humid areas for long periods of time. Compressors shouldn’t be left open to the atmosphere for longer than 20 minutes.
When you have too much moisture in a system it can create acid in that system which usually leads to a winding failure. One way to tell if there was too much moisture in the system if you see or notice copper plating inside the compressor.
It is essential that all foreign contaminants be removed from the system at the time of the original installation. Filings, shavings, dirt, solder, flux, metal chips, bits of steel wool, sand from sandpaper, and wire from cleaning brushes have all been found in systems and frequently end up in the compressor. Many of these contaminants are so small they will pass through a fine mesh screen. In addition, the metal fragments may be rotating because of gas velocity and cut or break the usual compressor suction screen.
Another step is to have a clean system before the operation which is to properly evacuating the system. Air and moisture are very detrimental to any refrigeration system and must be removed before start-up. Blowing out lines with dry nitrogen may remove a major part of the air from a system, but if any air is still trapped in the compressor during installation it is practically impossible to remove from the compressor crankcase by purging with nitrogen. New and replacement compressors are shipped from the compressor factory with a dry air holding charge and must be evacuated before being put in service. A triple evacuation of the system or compressor may be required and is recommended (twice to 1,500 microns and finally to 500 microns,) breaking the vacuum each time with dry nitrogen. The vacuum pump must be connected to both the high and low sides of the system through properly sized connections, since restrictive service connections may make the process so slow as to be unacceptable, or may lead to false readings because of pressure drop through the fittings.
Source: AE24-1105 – Principles of Cleaning Refrigeration Systems – https://webapps.emerson.com/online-product-information/Publication/LaunchPDF?Index=AEB&PDF=1105
HVAC School – How to Evacuate an AC system, Full Vacuum Procedure – https://www.youtube.com/watch?v=JsnQeUSuUMU