How much R-134a pressure is needed to activate compressor? (99 Grand Cherokee LTD) - JeepForum.com
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Unread 06-11-2006, 02:23 PM   #1
Ntruder
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How much R-134a pressure is needed to activate compressor? (99 Grand Cherokee LTD)

So I have no A/C, (that is, hot air only)

I have reasonable R-134a pressure. (25-30psi low side @ 65 degrees ambient) but the compressor won't turn on. I have never yet seen the center pully spin. It does move freely if I attempt to spin it with the engine off, but when I crank the A/C, it does NOT spin. (clutch is not engaging I suppose)

So here are my questions: (keep in mind, 99 Grand Cherokee limited, V8)

1) How much refrigerant pressure is required to turn on the compressor?

2) Where is the fuse/relay/power supply for the compressor?

3) Is there a good way to test the compressor's functionability? A way to check to see if it is capable of working? (ie: modify its power source switch to allow power to pass) I know that the compressor won't run with low refrigerant, and since I'll need the compressor running to recharge, logic would tell me that there's a way to turn on the compressor with low refrigerant pressure.

the vehicle is in near immaculate condition, and I would doubt that the compressor is junk. It would seem more likely to be an electrical problem, the condensor not being turned on, or something.

Any help?


Last edited by Ntruder; 06-11-2006 at 02:50 PM..
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Unread 06-11-2006, 04:37 PM   #2
GreenDean
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I beleive R134 systems need to be charged to 42psi.
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Unread 06-11-2006, 08:20 PM   #3
Turbonut
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25-30 psi with the compressor off means that there is not enough gas in the system. The 25/30 psi number is when the compressor is running, which means maybe 80 psi when off. Jump the low pressure switch on the accumulator and start the Jeep. The compressor will turn, then put in the gas fast. It's not in the best interest of the compressor to keep it turning when low or no gas as the oil will not circulate. Also keep in mind, if low, the gas has been lost somehow, so a leak is in the system.
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Unread 06-12-2006, 11:02 AM   #4
Ntruder
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The low side pressure needs to be that high with the compressor running? Ah I see.

Two questions:

If the R-134a level is too low, and because the R-134a provides lubricant for the compressor, the compressor will NOT turn on for defrost mode either, correct? So low pressure could explain why the compressor never goes on, even for defrost mode?

Next, this might be a stupid question, but I kept reading that statement (jump the switch on the accumulator) and was a little confused. IIRC, the accumulator is the cylindrical object on the low pressure side between the compressor and the evaporator, which is under the dash somewhere. There is a plug coming off the top of the accumulator which I can only assume connects to some kind of mechanical switch inside the accumulator. I'm guessing you mean jumper the vehicle-side plug end so it completes the circuit, therefor mimicking an open switch?

Also, the fact that there is pressure leads me to believe that if any leak, its very slow, perhaps simply a gradual leak over several years. I know R-134a can even permeate through the hoses over time. The oil in it is suppose to barricade it, but it will still slowly leak out over a long enough period of time. Either way I'll charge the system with a UV dye, and search for any signs of leaks. If its slow enough that I simply need a recharge every couple years, I can live with that. (it is a little inconvenient considering R-134a is not sold in my state, but I'll live)

First step either way is running the compressor.
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Unread 06-12-2006, 04:48 PM   #5
Ntruder
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Nevermind, I figured it out. I added a can, and now have about 35psi with the compressor running, and very cold air. Thanks for the help guys
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Unread 06-12-2006, 07:55 PM   #6
Turbonut
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Quote:
Originally Posted by Ntruder
Also, the fact that there is pressure leads me to believe that if any leak, its very slow, perhaps simply a gradual leak over several years. I know R-134a can even permeate through the hoses over time. The oil in it is suppose to barricade it, but it will still slowly leak out over a long enough period of time. Either way I'll charge the system with a UV dye, and search for any signs of leaks. If its slow enough that I simply need a recharge every couple years, I can live with that. (it is a little inconvenient considering R-134a is not sold in my state, but I'll live)

First step either way is running the compressor.
Glad you've got it running. Systems that were converted to 134 can loose gas through the hoses, but factory 134 lines are lined to not allow the gas to escape.
The Pag oil doesn't barracade the loss, it's there for compressor lubrication.
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Unread 06-12-2006, 09:57 PM   #7
sharksfan72
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I just talked to a buddy of mine that I work with. He used to work on cars and said that on the R-134a systems that the couplings and the compressor are the most common and probable place that the system would be leaking from.
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