AC pressure, compressor not running

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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?
 
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?
 
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!
 
At least it still HAS pressure
smile.gif
. Jumper the clutch to 12 volts and (quickly) check the pressure. Don't let run long.
 
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Readings taken with the compressor not running are only useful to know whether or not all the refrigerant has leaked out.
 
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.
 
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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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