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Compressor Flushing and Testing Procedure

bohica2xo on Wed October 13, 2004 8:37 PM User is offline

Compressor flushing and testing

There are a few reasons to flush your compressor.
1) If you are changing refrigerants, and need to use a different oil due to compatibility issues.
2) If you are working on an unknown system, that may be contaminated with unknown products.
3) You are using a compressor from a salvage yard with an unknown history.
Flushing a compressor on the bench

Here is the process for flushing a compressor. This compressor was removed from a 1986 mustang in the salvage yard. It is the original compressor, and the car had over 100,000 miles on it. The rust stains are evidence of a blown water pump - I am sure this car had been overheated several times.
A compressor must be flushed with the lubricant you intend to use in the system. Do not use any other flushing agent or solvent - you could damage your compressor.
First, let's add some oil to the suction port:

You should add 15 to 20 cc's of the oil you will be using in the system to the suction port. If you are working on an A6 or York type compressor, you will need to drain and refill the sump on the compressor as well.

Then mount the compressor in a vise, or hold it on a firm surface. You can turn it over with a socket and a speed handle like this:

Or, you can use a cordless drill. If you use a power tool, keep the speed below 150 revolutions per minute. Use a low torque tool like a cordless drill. Do NOT use a high speed tool, or an impact wrench. Rotate the compressor 10 to to revolutions.

Now crank away, but be careful. The oil will come out of the discharge port under pressure - this is a compressor. You will need to recover some of the oil to determine how dirty the compressor is. Make sure you collect and dispose of the oil properly.

Is it dirty?

A clean paper towel makes checking the oil condition simple. If your oil looks like this, then you need to flush some more. This was the second 15 cc's in this compressor.


I have found the following process good for evaluating a compressor's overall health.

There are bench tests involving dead-ending the high side, and measuring the pressure. When done to the specfic manufacturers instruction, that is a fine test. The down side is that you can build dangerously high pressures, or even open the relief valve if not done corectly.

The process I am describing uses the low side vaccuum as a benchmark instead. By using a fitting to block the suction side, and measuring the vaccuum developed you can check the condition of the cylinders, and the reed valves.

When I removed this compressor I also removed a short piece of the suction line. I plugged the end of the suction hose, and instaled it on the compressor. To test your compressor, you will need to make up some sort of fitting to attach your gauge set to the suction port. Since we are only dealing with vaccuum, you can safely epoxy some fittings together.

This compressor appears quite healthy. Within 10 revolutions, it showed 22 inches of vaccuum on this gauge set. The camera flash makes the micron gauge hard to read, but this pump actually managed to pull down to 1000 microns.... This is why you can't trust the vaccuum scale on a manifold set.

This compressor is quite healthy. It managed to stay under 5000 microns after 10 minutes - with the discharge port open to the atmosphere! The reed valves in this unit seal quite well, and the pistons seal well enough to pull down to 1000 microns.

Edited on 10/21/04 to add:

The testing portion of this post does not appear to work well with variable displacement type compressors, such as the V5 type. It is also not a valid test on any scroll type compressor, since they do not have valves on the suction side of the pump. Both of these types of compressor can be quite difficult to test, and should simply be replaced if they are suspect.

"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Edited: Fri November 16, 2007 at 11:10 AM by Automotive Air Conditioning Information Moderator

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