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Expert help needed PLS!

Posted: Thu Aug 29, 2019 7:01 pm
by BSTactics
Experts needed: My car is a 2004 Cavalier. I've replaced the compressor (reman), oriface, high/low pressure sensor and receiver/drier along with throughly cleaning the rest of the system.

I've tested all the wiring from the pressure sensor to pcm, compressor to relay, relay to fuse, fuse to batt, relay to pcm, pcm to ground, pcm to bcm.

There is a resistor in the wiring for the compressor. It connects the power side to ground that I couldn't read any resistence from so I've tried 2 used ones as well. Never got any readings from the 3 but I believe that's more of me not knowing what setting to use on my DVOM instead of faulty resistors. From what I've learned, that resistor is only there to absorb some of the energy during disengagement from damaging the pcm & coil.

Also, my compressor coil shows 4 ohms when checked.

My static pressure is about 80 once both sides has equaled out.

The compressor will engage if I jump the relay so I believe my issue is being caused by the pcm somehow.

The pcm/bcm has been reset multiple times as well.

Is there anything else I can do before giving up and paying a shop?

I do have some software and a bluetooth elm device but the only thing I have been able to find there is that the pcm reports "AC refrigerant: not available/completed."

Also, I've tried swapping over to a different computer/bcm with no luck there as well.

It doesn't display my AIT sensor right either so I'm thinking the 2 are related somehow because I have a good reference signal to it and I checked for continuity between the sensor and pcm but it still doesn't work.

Other than the AC and AIT sensor, the car doesnt have any other issues.

Sorry it's so long, just wanted to be detailed and thanks in advance.

Re: Expert help needed PLS!

Posted: Fri Aug 30, 2019 8:13 am
by Dougflas
Are you sure that is a resistor in the circuit of the compressor and not a diode?

Re: Expert help needed PLS!

Posted: Sun Sep 01, 2019 4:19 am
by GM Tech
It is a diode- J cars used diodes in compressor circuit.

Since you can engage compressor by jumping relay, it is obvious your issue is upstream. Look at the high side transducer- you know it is a transducer because it has 3 wires (upside down near top of radiator) look for wires loose, broken, also you can test voltage while connection is plugged in there. black will be ground, one will be constant 5 volt, and the other will vary from 0-5 volt depending on system pressure. approx 1 volt = 80 psi. So sitting at ambient not running, you should see about 1 volt. If these voltages are outside the parameters, the ecm turns off the compressor.

Re: Expert help needed PLS!

Posted: Tue Oct 01, 2019 9:21 pm
by BSTactics
Thanks for the replies. My transducer has continuity, 5v ref, & good sensor so I believe that area is fine. I don't know for sure, no scan tool to see what's going on in there. As for the diode, it probably is one. I wouldn't know the difference. Just some small little electrical thingy. Lol. Guess I need to Google that one.

As for the car, my air intake temperature sensor hasn't worked since I got the car. I believe this is my hang up. I'll know after tomorrow for sure, finally gonna try to finish this project and fix that circuit.

I had jumped the compressor with +12v to grd and ran it that way for 45 mins. Ac worked great till I stopped and the system made some weird hissing sound while blowing R134a out from somewhere. (Huge cloud came out from under my car) Once that stopped, I checked the pressures and it still had good static pressure. I'll recheck it tomorrow to make sure. I'm guessing the compressor has some sort of relief valve but into it to prevent it from exploding? I'm assuming my weights will be off for refrigerant/oil so I'll probably need to pay to have to emptied/refilled again? Anything else I need to worry about since that happened before I try using the compressor? I have an old compressor with a good clutch on it that I plan on using as a tester in order to get the rest of the car working again before I pay to have it emptied/filled.


Re: Expert help needed PLS!

Posted: Tue Oct 08, 2019 1:57 pm
by JohnHere
If I understand correctly, everything that GM Tech mentioned checks out. So it doesn't appear that the ECM is shutting off the compressor for any of the reasons cited. I'm not sure whether the intake air temperature sensor has anything to do with the compressor not engaging, but I'd go ahead and replace that first and see what happens. If the new sensor doesn't fix it, I'd install the old compressor with the good clutch next.

I should mention that jumping the compressor directly to battery voltage is never a very good idea. If you're going to do it anyway, it should be done momentarily, and never for as long as 45 minutes. In this instance, you effectively bypassed the system's fail-safe mechanisms, causing the compressor to build pressure to a very high and dangerous level. That's why the over-pressure valve popped off, releasing some refrigerant as well as oil. How much refrigerant and oil came out is anyone's guess, but you'll have to put back in probably at least a couple of ounces of oil. If you run the system without enough oil, the compressor won't last very long.

The specs for your vehicle call for 24.0 ounces of R-134a and 5.0 ounces of PAG-46.