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aggravation 08-14-2009 12:15 PM

pressure test ac compressor
I have my compressor out of the car and want to test it for leaks.
I'm hoping I can plug the two refrigerant line connection points somehow and then use one of the other schraeder valves to pressurize it.
Do I need to use both valves or will either pressurize the whole compressor?
How much pressure is enough?

tveltman 08-14-2009 12:49 PM

One valve will pressurize one side, the other will, of course, pressurize the remaining side. If you only pressurize one side (guessing here), you may cause the compressor to rotate. If you use a manifold and pressurize both sides equally at the same time, the compressor should not rotate. You would want to open both valves (on the gauge manifold) all the way, then add pressure from a compressed source. I don't know what limit to set, but obviously the compressor is designed to run high-side pressures typically around 150 PSI (although actual pressures can be significantly higher on a hot day), so I certainly would not go above that limit. My guess is both sides of the internals would withstand the same pressure, so I would say maybe to 100 or 125 PSI. This would give you ample pressure to test the valves to see if they are leaking, and the front seal as well. I would, however, gradually increase the pressure. Don't just dump 150 PSI into the compressor. Start ramping up to 40 PSI (the typical low side pressure) and see if it leaks. If it does, you can find your leak with soapy water over the outside. If no leak, increase to maybe 50 or 60, and repeat. Hopefully someone here can offer better guidance, but that is what I would do in your situation if I didn't have any better advice. good luck!

EDIT: If you have a lathe, you can produce an adapter to connect your compressor hose fittings to your charging manifold, and this will allow you to test the valves themselves.

dprantl 08-14-2009 04:28 PM

Trying to pressure-test a compressor is usually a futile process. The compressor is just like any other piston engine, so you have no idea if the valves are open/closed. Also, most compressors will leak from the shaft seal, which may only leak when the shaft is spinning fast. Since most compressors don't have that many seals anyway, it's better to just replace them all instead of trying to figure out how to test it. The 6E171 has three large body O-rings and a shaft seal.

'91 928GT S/C :eek: 475hp/460lb.ft

tveltman 08-14-2009 04:44 PM

I think that he was primarily concerned about the front main seal and the schraeder valves, which, I think, should either leak or not, regardless of what is going on with the compressor internals. Alternatively, he could rotate the unit by hand while under pressure (yikes!) and see if it makes a difference. I agree with you, though, it seems like it would be much easier to just swap all the seals. One of the easier places to check for a leak is at the seals where the hose manifold plate meets the actual compressor body. There are two o-rings between the plate and the compressor. I was able to find a pretty close o-ring from a local pepboys, and I've not had any leakage problems so far.

aggravation 08-14-2009 08:30 PM

Yea, just wanted to test the front seal. I'm replacing the O rings through out the whole system but don't have a seal for the shaft so I thought I might be able to determine if it is really needed which would mean waiting for it to be shipped... or if I can go ahead with the reassembly tomorrow just doing receiver/drier and TXV along with the O rings.

dr bob 08-14-2009 08:40 PM

just replace the seal. You'll invest more time, effort and worry in your test fixture than you will in the new seal. Just do it!

ZEUS+ 08-14-2009 09:11 PM

After rebuilding my compressor, I clamped a hose to both ports. Vacuumed down and it held for 30 minutes. Has been performing well ever since rebuild.

aggravation 08-14-2009 09:56 PM

Originally Posted by dr bob (Post 6816493)
just replace the seal. You'll invest more time, effort and worry in your test fixture than you will in the new seal. Just do it!

I knew someone would come in here and shame me with common sense ;) It is pretty embarrassing that I'd order a replacement TXV to replace one that worked fine but didn't order the seal...
OK, so is there any chance the seal is of a generic specification that a local auto parts store might have one on the shelf?

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