HVAC, experts, HELP

[a64pilot]

Problem, after work Sat. I cranked up the truck, waited to the voltmeter read 14, turned the A/C on high and bumped the idle to 1200. Have done this many times with no problem.
Any way in about 30 sec. I hear a loud pop and hiss with whiteish smoke coming from under the hood. I immedately shut down thinking I have blown an A/C line. It appeared that the back side of the compressor vented some refrigerant as there was oil behind it. It wasen't still leaking though. I theorize maybe the expansion valve had clogged making the high side pressure go through the roof, and is there a high pressure safety valve in the back side of the compressor? All appears to be functioning normally now but low on refrigerant. My low side pressure is 30 psi and high side around 145, this is at 81 deg.
What should my pressures be? What happened? How do I prevent a reoccurence?

[DWB]

Have had similar problem. The dealer replaced compressor and according to them, on a 81 deg day, pressures should be 50-76(low)and 147-226(high). I've noticed my A/C does not put out very cold air after the temp gets up over 95 deg. Did you have same problem (before freon leak)?

[a64pilot]

DWB,
No not at all, you could hang meat in my truck. Of course the humidity difference between the desert and L.A. (lower alabama) is enormous, and I think A/C works better in high humidity conditions.
Are your cabin filters clean? If you have a newer 03, maybe your evaporator is dirty if you drive in real dusty conditions?
I was looking for pressures to re-service my A/C to. I went to I think 215 and 45 IIRC, it sounded high but I was not getting any compressor cycling and seemed to be working correctly, just wanted validation that I didn't overservice it.

[a64pilot]

DWB,
I don't know how to edit now so I had to repost.
Anyway since they had your A/C system open, maybe the didn't pull a good enough vacuum before they reserviced it. Might be worth paying someone else to evacuate and re-service your A/C.

[DWB]

a64pilot,
The pressures came off the TSB the dealer printed out showing accepable pressures and vent temp for 03' Duramax. Keep in mind that the same TSB says 81 deg. is an acceptable vent temp when temp is 102 w/ 22% humidity. I don't think so!!

[a64pilot]

Can anybody at least tell me what happened to the compressor? Is it junk now or was this some weird thing that will not likely to re-occur.

[DinoMax]

a64pilot, there is a pressure relief type valve on the back of the compressor. It's designed to bleed off when head pressure gets too high. Not sure why yours suddenly had a surge in pressure, but it usually means there is a blockage/restriction somewhere in the system, or it was over/undercharged w/ freon (obviously not your case when this happened). It is a good idea to bring it to an A/C shop & have the system properly vacumed down to nothing, then re-charged to spec. pressures. It is possible to build up high head pressure when system is under or over charged. When they vacum down and recharge, they should be able to detect any blockage or restriction, if any, that you have. Hope this helps smile.gif DinoMax

[a64pilot]

Thanks DinoMax I thought something like that. I'm liscensed and have a vacuum pump, but no recovery system. It has been operating normally for a while now, shouldn't have beeen overserviced as it has been fine for almost two years and hasen't been touched since new.
Am I correct in assuming that the most likely place for a stoppage is in the expansion valve?

[DinoMax]

a64pilot, yes, the expansion valve is the most likely place. A good way to tell if you have a blockage or restriction is to look at your a/c lines. I've seen them ice up around the outside in this situation (due to the freon not flowing freely), which would indicate a blockage, and result in the higher head pressure. Also, check your radiator coolant level. I've experienced this problem in a number of makes & models in the past (I'm in the used car business). If your coolant level is down, your engine operating temps go up, which will in turn create more engine compartment heat, and that could also increase head pressure at the a/c compressor. Just a thought, hope you get it figured out. DinoMax

[a64pilot]

DinoMax,
Thanks, but the darn thing has been working fine (so far). I think a piece of an O ring got caught in the expansion valve or something and has passed along down stream.