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Why does the replacement compressor use different oil (than the original unit)

By Richard Hawkins, MACS Contributor

Let’s look at a different (but equally important) area of compressor lubrication.  That is viscosity and specifically why a replacement compressor might use a different viscosity oil than its OEM counterpart.

The question coming into the tech line often goes something like this: ” I have a compressor I’m ready to install and need some clarification on the oil that should be used in it. The label on the vehicle has an OEM part number on it that interchanges to PAG 150 and my information system also lists that same number.  My supplier sent me a bottle of PAG 150, but the label on the compressor calls for PAG 46.

What is going on here, I’m confused?”

And then the conversation goes something like this:

Me:  Can you please give me the vehicle application and compressor part number and all the information from the label on the replacement compressor?

Technician:  Sure, it is part number ______ and the manufacturer is _______ and it says: Made in ______. This compressor contains 8 ounces of PAG 46 oil.

Me:  OK. That is the correct part number for the vehicle and PAG 46 is going to be the correct oil.

Technician: Are you sure? I do not mean any disrespect, but proper compressor lubrication is so important and there were three things indicating the need to use PAG 150 and only one indicating PAG 46.

Me:  Yes, I am sure as I am familiar with that compressor and the manufacturer and that same question has come up numerous times.  Also, I applaud your cautious approach. 

Technician:  I feel confident with your answer as it sounds like you have done some research on it previously, but why does this situation exist?

Me:  Because the manufacturer of this replacement compressor uses a different internal design (or “gut pack” as it is so fondly called sometimes in the industry) than the OEM compressor manufacturer and the different design calls for a lighter weight oil. If you were to take apart both the original compressor and the replacement compressor and compare them, they would look totally different on the inside. It is even possible that the number of cylinders might be different, although the displacement will be about the same.

Your information system of course is going to have OEM information and your supplier sent you the PAG 150 because it is the oil that is listed for the OEM compressor.  As most A/C parts suppliers have multiple sources on compressors, it is also possible that you could have received a compressor that did indeed call for PAG 150 or even PAG 100 which uses an additional different internal design, so it is wise to be cautious.

Technician:  Wow. Things sure are a lot more complicated than they used to be. Thanks for the information and taking the time to explain all of this.

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