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Compressor Oil Fill

oil fill
(illustration: Sanden International)
Richard Hawkins is a technical advisor at 1-800-Radiator. He recently told MACS about a question he received from one of the company’s franchise offices.
I cringe whenever I hear a technician say that he puts ALL the oil into a system using a recovery/recycle/recharge machine. When you use a machine to install oil, it’s putting the oil in through the high-side service port, and it takes a long time for the oil to make its way around to the compressor – where it needs to be. If the service port happens to be located on the discharge line right at the compressor, and if it’s an expansion valve system, the oil must travel through the discharge line, through the condenser, through the drier, through the liquid line, through the expansion valve, through the evaporator, and finally through the suction line before it ever gets to the compressor. That can take a while to happen, and when the oil does get there, it will take a while for the proper amount to accumulate in the compressor.
Even if the high-side port happens to be located on the liquid line near the expansion valve, the oil still has to travel through the expansion valve, evaporator and suction line to get to the compressor, and oil doesn’t travel very fast through an expansion valve that might have an opening of only 0.035 inch. This is the worst way to install oil in a system (not to mention that the oil may be the wrong viscosity, because the machine might have PAG 46 in it and the compressor might call for PAG 150).
R/R/R machines were really only designed to put a small amount of oil in a system, to replace some that might have been removed during service, not to put in a full charge. The vast majority of the oil should be put directly into the compressor. It’s the only part in the system that requires lubrication.


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When having your mobile A/C system professionally serviced, insist on proper repair procedures and quality replacement parts. Insist on recovery and recycling so that refrigerant can be reused and not released into the atmosphere.

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