Question about 1986 Pontiac Firebird

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AC compressor will not energize

Ok, I have an 86 Firebird with the 2.8 V6 and an auto trans. The AC system was dry for some time, so it was recharged with R134a. My issue is this. If I pull off the plug on the low pressure switch and jump the contacts in the plug, the compressor will not engage. However, if I attach a test light to ground and probe a wire on the AC control relay, the compressor kicks in and will run until I remove the ground. I used the test light to verify power going to the low pressure switch and there is. No power to the compressor until I ground the relay. The relay will then click and engage the compressor. There is 24 oz of R134 in the system now. This should be enough to cycle the compressor but to no avail. I am lost as to what the problem could be as I have heard simply jumping the low pressure switch will make the compressor energize and it does not. If the relay was bad, it would not click and engage when grounded. What else could it be?

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First thing you should check is all your grounds, on the body and your battery connections. Also double checked to make sure you have the air conditioning on with the fan on. If this is good the next thing to do is to get a wiring diagram. Verify that there's power going into the switching and coming out of the switch. Next find the compressor relay verify that there's power going two it. If this is good use your tests light to ground out the relay. If this works find out where the ground wire goes to the computer or the wide open relay. Good luck.







Posted on Jul 18, 2010

  • sidewinder98 Jul 18, 2010

    There is power at the relay. I am not sure what else it could be.

  • Fixer dude Jul 19, 2010

    OK so you have a jumper wire in your pressure switch plug. To energize the relay for the compressor you need power going in, and a ground for that, the ground may go to the computer so the computer can control the compressor or the wide open throttle relay which turns the compressor off while giving it full throttle. Use your test light to test this area because some relays have diodes in them which can burn out easily. Good luck.

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