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It's never as easy as you think...

msplat81 on Wed July 28, 2010 11:29 AM User is offlineView users profile

Year: 1997
Make: Chevy
Model: Monte Carlo
Engine Size: 3.1
Refrigerant Type: R134
Ambient Temp: 90
Pressure Low: 50
Pressure High: 50
Country of Origin: United States

I'm on AC repair, but I've fixed most things on my car, so I gave it a try. I had a leaking compressor at a seal. I figured I'd buy a used compressor (V5) off of ebay with a 30 day warranty. I purchased a new dryer/accumulator and orifice tube as well. I then bought a vacuum pump and gauges from Harbor Freight.
Checking my system, it was completely empty (0 psi) of refrigerant so I didn't have anything to collect. I pulled and replaced the compressor, accumulator, and orifice tube. There was absolutely no oil in compressor or tubes or accumulator.

1. Added 3.5oz oil to the compressor. I added it to the high pressure side and turned the clutch to get it to go in. I hope that's okay. (PAG 150)
2. Added 2.5oz oil to the accumulator.
3. Added 1.0 oz to the hoses between the compressor and accumulator.
4. Changed the orifice tube.

I did not flush the system (probably not my best idea) since the compressor was not broken, and I didn't see debris. I then put it all back together and pulled a vacuum on it for 40 minutes. Then the blue low pressure gauge read -30 and the red high pressure gauge read 0 (or as low as it goes). I let it sit for 20 minutes, and I still had a vacuum. At this point I thought I was good to go since I had a constant vacuum.

I had a 2/3 can of refrigerant with UV dye left over (used to locate original leak a few months ago). Unfortunately I didn't have the adapter to hook this line up to the gasket inlet, so I unplugged the gaskets and put this can with its walmart gauge on the lower pressure line. I started adding the refrigerant with the car running and AC on full. The low side pressure got up to about 50psi with roughly 8oz of the can, then I stopped. The compressor clutch did not kick on. I figured this was due to the low amount of refrigerant. I grabbed some extra wire and jumped it from the battery and the compressor kicked on fine. But what I noticed is that the pressure in the low side would drop from about 50 to 30 while the compressor was on, but once disconnect the pressure would return to 50psi. I gave up for the evening due to demands of homework.

The next morning, I went and got an adapter for the refrigerant line and hooked up the gauges to the low and high sides again. After sitting overnight the pressure has equalized in both the high and low at 50psi. I did not add anymore freon, but I played with the clutch a little and saw that when the compressor was jumped the low would drop to 30 and the high would increase to about 75. But again as soon as I disconnect the clutch, everything would return to 50psi. I did this a couple of time for about a minute each.

So is that the compressor not bringing the refrigerant to the high side? What should I do here? I don't know why the pressure is not dropping on the low and raising on the high. Thanks for your advice/help!

mk378 on Wed July 28, 2010 11:43 AM User is offline

The V5 has an oil sump. You needed to open the oil plug in the side, dump the old used oil, and put new oil in there! Now there is a major oil problem which can likely only be resolved by flushing the system and starting over.

Pressures look right for a V5 system that contains very little refrigerant. Realize that the compressor will never pump the low side much below 30, as that is what the variable feature is designed to do. Do not jump the compressor.

msplat81 on Wed July 28, 2010 12:28 PM User is offlineView users profile

So is there too much oil in the system? Is that due to old oil in the compressor from ebay? I checked it for oil and didn't find any, but I suppose it is possible since I'm new at this. I'll flush it out. Just curious. What would be the amount of oil you would add to the compressor, accumulator, etc..?

GM Tech on Wed July 28, 2010 2:22 PM User is offline

You checked for oil where? Check in the oil drain bolt on belly of compressor--- add and remove oil there-- there is always 3+ ouncesin there at any given time--- do not add oil in the ports of a V-5.....

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

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