2001 Malibu AC compresser relay jump - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 06-24-2015, 02:18 PM   #1
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Default 2001 Malibu AC compresser relay jump

Hello Guys,
I am working on a 2001 Malibu AC. Switches and controls all seem fine but compressor won,t come on. I'm thinking this is because it'* low on freon. In order to check freon I need to have compressor running (I think). So I have pulled the relay in order to jump start compressor but I don,t know which terminal to jump too.The diagram on side is Greek to me. the numbers on the side are 86,87,(top) 85,30(bottom) if that means anything to anyone.
Also what should I see in sight glass if freon is low. Thanks for any help with this. It' 98 degrees outside.

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Old 06-24-2015, 11:36 PM   #2
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If the refrigerant is low, the pressure at rest should be about 125psi at rest. You'll be able to see that with the high side gauge, and the low side should max out (they usually max at 100psi). That should be enough pressure to get the compressor to start, and then the low side pressure will drop rapidly until it kicks out because the pressure drops to low, in the 10-20psi range. If the sight glass is on the high side, I believe you are supposed to see solid liquid, no bubbles.

If the gauge is reading lower than according to this chart: Refrigerant Pressure - Temperature Chart for R-134a, than there is likely nothing in the system, or so little that it'* only pressurized gas and no liquid. If it has no pressure at rest, than there is the possibility outside air has now contaminated the system, in which case you should track down the issue and resolve it, replace the drier, have a vacuum pulled on the system for 30 min to pull all of the moisture out, and then properly charged.

You are correct, pressures should be observed when the compressor is running, but you can see enough without it running as outlined above to try and figure out why it is not running. Causing a compressor to engage with no safety measures is a great way to cause more damage.
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Old 06-27-2015, 11:41 PM   #3
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What sight glass?

You don't need the compressor running........the pressure on the low and high side should be equal, without it running....should be equal to ambient temp, on a cold engine.....for example, if 70F ambient air, should have 70 PSI on both hi and low side....think you have to have a min of 45PSI to start.....

Another thing to check would be codes.....this system uses a pressure sensor....if pressure is too high, or too low, the compressor will not be enabled by the PCM(normal pressure signal is 1.5 volts DC).....pressure could be ok, but if you have a bad sensor, or bad wire harness to the sensor, giving incorrect data to the PCM, the compressor will not be enabled.......P0530 may be set....

Check this out:

DTC P0530 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit
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Old 06-28-2015, 09:20 PM   #4
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Thanks for the info guys.I think I'm going to have to let a pro handle this one. The low pressure port on this car is in a difficult place to get to with Micky Mouse gage that comes with freon from Wal Mart. I did manage to get enough freon in it to start compressor but still not cooling.I'll let someone who has right equipment check it. Thanks again
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