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#4474295 - 07/30/17 01:28 AM AC pressure, compressor not running
slowdime Offline


Registered: 09/17/13
Posts: 429
Loc: 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?
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#4474298 - 07/30/17 02:15 AM Re: AC pressure, compressor not running [Re: slowdime]
Merkava_4 Offline


Registered: 01/30/07
Posts: 17501
Loc: Clovis, CA
The low pressure side is reading high because the compressor is not on.

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#4474324 - 07/30/17 03:35 AM Re: AC pressure, compressor not running [Re: slowdime]
LvR Offline


Registered: 09/19/09
Posts: 24
Loc: 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?

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#4474334 - 07/30/17 04:07 AM Re: AC pressure, compressor not running [Re: slowdime]
Shannow Online   content


Registered: 12/12/02
Posts: 39840
Loc: 'Stralia
Can't get the low side to 350 psi IMO.

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#4474383 - 07/30/17 06:55 AM Re: AC pressure, compressor not running [Re: Shannow]
Brad_C Offline


Registered: 07/27/12
Posts: 617
Loc: 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.

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#4474384 - 07/30/17 06:57 AM Re: AC pressure, compressor not running [Re: slowdime]
Trav Offline


Registered: 11/20/06
Posts: 18836
Loc: MA, Mittelfranken.de
VW?
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#4474449 - 07/30/17 08:33 AM Re: AC pressure, compressor not running [Re: Merkava_4]
Linctex Offline


Registered: 12/31/16
Posts: 6148
Loc: 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!
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#4474470 - 07/30/17 08:50 AM Re: AC pressure, compressor not running [Re: slowdime]
Chris142 Online   content


Registered: 06/05/03
Posts: 16814
Loc: 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.
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#4474502 - 07/30/17 09:39 AM Re: AC pressure, compressor not running [Re: slowdime]
KrisZ Offline


Registered: 12/23/06
Posts: 7456
Loc: Toronto, Canada
Is the clutch getting the 12v signal?
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#4474575 - 07/30/17 10:55 AM Re: AC pressure, compressor not running [Re: slowdime]
HerrStig Offline


Registered: 08/24/11
Posts: 9560
Loc: 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.


Edited by HerrStig (07/30/17 10:55 AM)

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#4474597 - 07/30/17 11:36 AM Re: AC pressure, compressor not running [Re: Trav]
slowdime Offline


Registered: 09/17/13
Posts: 429
Loc: Cascadia
Originally Posted By: Trav
VW?


Yup. A 2004 Jetta.
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#4474598 - 07/30/17 11:36 AM Re: AC pressure, compressor not running [Re: slowdime]
mk378 Offline


Registered: 09/27/15
Posts: 1414
Loc: USA
Readings taken with the compressor not running are only useful to know whether or not all the refrigerant has leaked out.

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#4474747 - 07/30/17 03:28 PM Re: AC pressure, compressor not running [Re: slowdime]
Trav Offline


Registered: 11/20/06
Posts: 18836
Loc: 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.


Edited by Trav (07/30/17 03:31 PM)
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#4474823 - 07/30/17 04:50 PM Re: AC pressure, compressor not running [Re: Trav]
slowdime Offline


Registered: 09/17/13
Posts: 429
Loc: 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.
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2010 Sentra PP & Wix

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