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No AC high high side pressure does not change when car is off.
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Homerbsharp
New User
Sep 7, 2010, 5:15 PM
Post #1 of 5
(7653 views)
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No AC high high side pressure does not change when car is off.
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Chevy prizm '98. 1.5 years ago there was a pinhole leak in high side and mechanics replaced compressor along the way - in winter. By summer it was cycling for too much pressure and I had it purged and filled professionally. This summer AC was working fine then over period of one day, no cold AC or cold pipes. No diagnostic codes for problem. Fuses look OK. Clutch is engaged. On a hot day in Texas, high side ~380 psi low ~35+. This stays relatively the same when the car is off. I would have thought this might be high side blockage, orifice tube, but I also understand high side would be low pressure if there was a blockage. I also thought that when the car was off the pressure between high and low would equalize but it stays the same... any ideas?
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Homerbsharp
New User
Sep 7, 2010, 6:53 PM
Post #3 of 5
(7640 views)
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Re: No AC high high side pressure does not change when car is off.
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Yes, the gauges stay the same when the car is off. When I started the car and let it run I did see some small fluctuation on the low side but only a few psi. The gauges go back to zero when disconnected, then back to 35 and 380 when put back on the system, and they held for two weeks in the garage while I worked on the car. The clutch stays engaged and does not cycle.
As for the condenser fan, I have two radiator fans and they are both working.
I am not sure how I would test if the gauges are getting full flow. I suppose I could try them on my other car and make sure I get normal readings.
My theory was that the compressor was pumping up the pressure, which could not flow through the system due to blockage, though I am unsure of the path taken for the pressure to equalize when the car is off. I was assuming that the compressor would close and the pressure would equalize through the evaporator but a high side blockage, my guess being the orifice tube, was preventing the equalization. The high side diagnostic connection is right before the connection where I believe is the orifice tube so that conveniently fit my theory. Then I read that a high side blockage would normally lead to low high side pressure so my lame theory was bust ...
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Hammer Time
Ultimate Carjunky
/ Moderator
Sep 7, 2010, 6:57 PM
Post #4 of 5
(7637 views)
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Re: No AC high high side pressure does not change when car is off.
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I have never seen anything hold pressure like that . Hook up a set of gauges and open both valves to equalize the pressures through the gauges and then close the valves and start it up and see if the gauges immediately react.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 7, 2010, 8:49 PM
Post #5 of 5
(7627 views)
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Re: No AC high high side pressure does not change when car is off.
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Same - never seen a system that locked high from low side so extremely. Don't understand why compressor doesn't plain shut down either? High pressure cut out should have made it quit but I bet an old two step cryo-silane sealer with moisture IN the system could probably do that and HPCO switch is so clogged it can't shut down compressor.
Something is all wrong of course. From what I see here you could vacuum down the low side and high side wouldn't change and that's not the way it works??
T
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