Odd AC problem

[marrt]

No AC. Mechanic hooked up some gauges. The compressor cycles normally. The low pressure side builds pressure then the compressor shuts off. The high pressure side will not build pressure. The system will not take any additional Freon. Any ideas?

[muddkatt]

Low side should not build pressure. The pressure should go down on the low side.

 

First question I have is what is both gauges reading when the compressor is off?

[marrt]

Thanks Muddkatt. Don't know the answer to that because I didn't see it. Just heard from the mechanic. He evacuated the system, "cleaned the orifice" and recharged the system. It's working now but...when first turned on, he's says the compressor is making a strange sound. It goes away after a bit and the AC works normally. I'm going down now to check. This is a 2002 GMC Sierra Denali with only 18K miles. The truck obviously set around a bit but is in near new condition.

[marrt]

Just got back from the mechanic. The AC now works. However, on startup after sitting a couple hours, there's a weird noise/vibration coming from the compressor or radiator just as the compressor kicks in. It only lasts a couple seconds but the high pressure tube even vibrates during this time. Eventually, it gets less and less with each compressor cycle and goes away. Maybe it's the compressor clutch slipping?

[sefiroxx]

Likely the compressor had "settled" in and the hard start is overcoming it. Plan on a compressor replacement.

 

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[muddkatt]

Too much PAG oil in the system will cause those vibrations. Liquids do not compress and will lead to compressor failure.