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How much compressor oil is too much?

By Richard Hawkins, MACS Technical Contributor

A lot of interesting calls are encountered when working on an A/C tech help line and a large percentage of them involve lubrication issues (probably somewhere around 25%). With that being the case, we plan to focus on a lubrication issue here and more in the coming weeks. 

A while ago, I had a memorable tech call with an inexperienced technician who thought he had a compressor problem. However, it was a lubrication issue, and it was extremely challenging convincing him.  The vehicle was a 2002 Chevrolet Tahoe with low mileage where just the compressor was replaced, because the clutch had somehow been damaged in an accident. The A/C system had been working fine before the accident but was experiencing some extremely high head pressures (365-375 psi) and it wasn’t cooling very well after the compressor replacement.  Since the compressor was the only component replaced, the technician assumed that the compressor was the source of the problem and he wanted it warranted to replace it with another unit.   

After getting all the information about the service work performed; pressures, ambient temperature, fan function, etc, I asked how much oil had been installed and the reply was 8 ounces. The next series of questions with answers were as follows:

1. Was there any oil removed from the system by flushing or blowing it out with air? No.

2. Did you drain the oil from the original compressor and measure it? No.

3. Did you drain the oil from the replacement compressor?  No

After doing a bit of quick math in my head, I replied: I think we have found your problem—-there is too much oil in that system. To which he replied: “That’s impossible. The book calls for 8 ounces and I put one 8-ounce bottle in. How can that be?”

To which I replied: “Yes 8 ounces is the correct amount, but you have about 22 ounces of oil in that system. The system was charged with 8 ounces of oil at the factory. You removed the original compressor. It probably contained about 2 ounces, so that left 6 ounces in the system. You installed a remanufactured compressor that contained 8 ounces. That makes 14 ounces so far. Then you added the 8-ounce bottle of oil. That brings the total amount up to 22 ounces.”   Then a long discussion took place about whether the compressor contained oil or not and the effects that a huge overcharge of oil can have on pressures. 

After a considerable amount of push-back, I was finally able to convince him that it was going to be necessary to reduce the amount of oil in that system to ever get the pressures down and get it to cool properly. When he did so, the system cooled much better.

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