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AC pressure, compressor not running #4474295
07/30/17 01:28 AM
07/30/17 01:28 AM
Joined: Sep 2013
Posts: 429
Cascadia
slowdime Offline OP
slowdime  Offline OP
Joined: Sep 2013
Posts: 429
Cascadia
I normally don't touch AC systems, but long story short, shop wanted $1000 to replace compressor and condenser when the only part that had failed was the compressor clutch. I replaced it myself and it's working great. My wife's cousin was over today as I was working on my wife's car and said her AC hasn't been working for quite some time. I hooked up the AC manifold I had purchased and the high pressure side was 150psi, but the low pressure side was 350psi. I was stumped and doubled checked to make sure everything was connected properly. It was about 108 degrees today. The compressor doesn't come on, fuse and relay seem okay, tested the compressor clutch coil for continuity and its okay. I asked if she had ever had it recharged, thinking someone may have added too much, and she said no. What on earth could cause such a high reading on the low side? Maybe the previous owner added some refridgerant?


2005 TrailBlazer I6 7qts of free M1 & Wix
2010 Sentra PP & Wix
Re: AC pressure, compressor not running [Re: slowdime] #4474298
07/30/17 02:15 AM
07/30/17 02:15 AM
Joined: Jan 2007
Posts: 17,501
Clovis, CA
Merkava_4 Offline
Merkava_4  Offline
Joined: Jan 2007
Posts: 17,501
Clovis, CA
The low pressure side is reading high because the compressor is not on.

Re: AC pressure, compressor not running [Re: slowdime] #4474324
07/30/17 03:35 AM
07/30/17 03:35 AM
Joined: Sep 2009
Posts: 25
SA
LvR Online content
LvR  Online Content
Joined: Sep 2009
Posts: 25
SA
Originally Posted By: slowdime
I normally don't touch AC systems, but long story short, shop wanted $1000 to replace compressor and condenser when the only part that had failed was the compressor clutch. I replaced it myself and it's working great. My wife's cousin was over today as I was working on my wife's car and said her AC hasn't been working for quite some time. I hooked up the AC manifold I had purchased and the high pressure side was 150psi, but the low pressure side was 350psi. I was stumped and doubled checked to make sure everything was connected properly. It was about 108 degrees today. The compressor doesn't come on, fuse and relay seem okay, tested the compressor clutch coil for continuity and its okay. I asked if she had ever had it recharged, thinking someone may have added too much, and she said no. What on earth could cause such a high reading on the low side? Maybe the previous owner added some refridgerant?
Doesn’t make sense .................

Compressor not running means the hp and lp sides should be at roughly the same pressures because the hp side bleeds down via the expansion valve to the lp side.


Stuck closed expansion valve and system in protection because of over pressure?

Re: AC pressure, compressor not running [Re: slowdime] #4474334
07/30/17 04:07 AM
07/30/17 04:07 AM
Joined: Dec 2002
Posts: 40,908
'Stralia
Shannow Offline
Shannow  Offline
Joined: Dec 2002
Posts: 40,908
'Stralia
Can't get the low side to 350 psi IMO.

Re: AC pressure, compressor not running [Re: Shannow] #4474383
07/30/17 06:55 AM
07/30/17 06:55 AM
Joined: Jul 2012
Posts: 663
Perth, Western Australia
Brad_C Offline
Brad_C  Offline
Joined: Jul 2012
Posts: 663
Perth, Western Australia
Originally Posted By: Shannow
Can't get the low side to 350 psi IMO.


Easy easy. Put the car in a paint oven. ~78C will do it.

Re: AC pressure, compressor not running [Re: slowdime] #4474384
07/30/17 06:57 AM
07/30/17 06:57 AM
Joined: Nov 2006
Posts: 19,934
MA, Mittelfranken.de
Trav Offline
Trav  Offline
Joined: Nov 2006
Posts: 19,934
MA, Mittelfranken.de
VW?


ASE L1, Master. Deutsch Meisterbrief.
Re: AC pressure, compressor not running [Re: Merkava_4] #4474449
07/30/17 08:33 AM
07/30/17 08:33 AM
Joined: Dec 2016
Posts: 6,259
Waco, TX
Linctex Offline
Linctex  Offline
Joined: Dec 2016
Posts: 6,259
Waco, TX
Originally Posted By: Merkava_4
The low pressure side is reading high because the compressor is not on.


Even the pressure in the can is nowhere near that high!


"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
Re: AC pressure, compressor not running [Re: slowdime] #4474470
07/30/17 08:50 AM
07/30/17 08:50 AM
Joined: Jun 2003
Posts: 17,364
Deplorable in apple valley, ca
Chris142 Online content
Chris142  Online Content
Joined: Jun 2003
Posts: 17,364
Deplorable in apple valley, ca
Ya you simply cant have that much pressure on the low side. The evaporator would have split open a long time ago.


02 Wrangler durablend 10w40
87 F250 traveler 15w40
04 Tahoe super-s 10w30
Z400 castrol T 10w40
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Re: AC pressure, compressor not running [Re: slowdime] #4474502
07/30/17 09:39 AM
07/30/17 09:39 AM
Joined: Dec 2006
Posts: 7,655
Toronto, Canada
KrisZ Offline
KrisZ  Offline
Joined: Dec 2006
Posts: 7,655
Toronto, Canada
Is the clutch getting the 12v signal?


2015 Dodge Grand Caravan-27k miles.
2006 Mazda 3-163k miles
Re: AC pressure, compressor not running [Re: slowdime] #4474575
07/30/17 10:55 AM
07/30/17 10:55 AM
Joined: Aug 2011
Posts: 9,560
Boston, MA
HerrStig Offline
HerrStig  Offline
Joined: Aug 2011
Posts: 9,560
Boston, MA
At least it still HAS pressure smile. Jumper the clutch to 12 volts and (quickly) check the pressure. Don't let run long.

Last edited by HerrStig; 07/30/17 10:55 AM.
Re: AC pressure, compressor not running [Re: Trav] #4474597
07/30/17 11:36 AM
07/30/17 11:36 AM
Joined: Sep 2013
Posts: 429
Cascadia
slowdime Offline OP
slowdime  Offline OP
Joined: Sep 2013
Posts: 429
Cascadia
Originally Posted By: Trav
VW?


Yup. A 2004 Jetta.


2005 TrailBlazer I6 7qts of free M1 & Wix
2010 Sentra PP & Wix
Re: AC pressure, compressor not running [Re: slowdime] #4474598
07/30/17 11:36 AM
07/30/17 11:36 AM
Joined: Sep 2015
Posts: 1,529
USA
mk378 Offline
mk378  Offline
Joined: Sep 2015
Posts: 1,529
USA
Readings taken with the compressor not running are only useful to know whether or not all the refrigerant has leaked out.

Re: AC pressure, compressor not running [Re: slowdime] #4474747
07/30/17 03:28 PM
07/30/17 03:28 PM
Joined: Nov 2006
Posts: 19,934
MA, Mittelfranken.de
Trav Offline
Trav  Offline
Joined: Nov 2006
Posts: 19,934
MA, Mittelfranken.de
Originally Posted By: slowdime
Originally Posted By: Trav
VW?


Yup. A 2004 Jetta.


Yep been there done that the readings are correct. Bad Sanden compressor, get one from Hella/Behr # HELLA 351125751 (best compressor for the money). You can sometimes replace the control valve but if it doesn't fix it its a PITA putting the compressor in and out again and again.
Replace the receiver dryer and expansion valve, there will be no debris from the control valve failure.

A word on the expansion valve on these, it uses 2 long screws that go into a clamp that attaches to the evap core, these screws are often seized, if they don't move with slight pressure forget it, just leave it.
I have had to cut a line with a cutoff wheel and mirror to get them out, its difficult and risky for the evap core.

Edit: PM if you need more info on this, there is a white temp switch in the cooling system that controls clutch operation and a few other things that tend to fail.

Last edited by Trav; 07/30/17 03:31 PM.

ASE L1, Master. Deutsch Meisterbrief.
Re: AC pressure, compressor not running [Re: Trav] #4474823
07/30/17 04:50 PM
07/30/17 04:50 PM
Joined: Sep 2013
Posts: 429
Cascadia
slowdime Offline OP
slowdime  Offline OP
Joined: Sep 2013
Posts: 429
Cascadia
Originally Posted By: Trav
Originally Posted By: slowdime
Originally Posted By: Trav
VW?


Yup. A 2004 Jetta.


Yep been there done that the readings are correct. Bad Sanden compressor, get one from Hella/Behr # HELLA 351125751 (best compressor for the money). You can sometimes replace the control valve but if it doesn't fix it its a PITA putting the compressor in and out again and again.
Replace the receiver dryer and expansion valve, there will be no debris from the control valve failure.

A word on the expansion valve on these, it uses 2 long screws that go into a clamp that attaches to the evap core, these screws are often seized, if they don't move with slight pressure forget it, just leave it.
I have had to cut a line with a cutoff wheel and mirror to get them out, its difficult and risky for the evap core.

Edit: PM if you need more info on this, there is a white temp switch in the cooling system that controls clutch operation and a few other things that tend to fail.


Thanks Trav.
I'll talk to her, she's a bit of a tight wad and may not want to put any money in to it. It's over 100 degrees here every day in the summer though, she may change her mind.


2005 TrailBlazer I6 7qts of free M1 & Wix
2010 Sentra PP & Wix

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