Question about 1981 Chevrolet Corvette

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I have a 1991 corvette the a/c compressor wont run unless i apply 12 volts direct to it i jumped out the high pressure switch. Is it controlled by an ecm? What are some other things i can try?

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  • webmasterrip May 13, 2009

    yES I HAVE A GOOD CHARGE ITS AN ELECTRICAL PROBLEM. I meant to say i jumpered the high pressure switch and there was no change so i dont believe that to be the problem

  • webmasterrip May 13, 2009

    sure i'll work with ya, I dont mind paying i wish the chat window was working so i could pick someones brain. Dont know how to fix that either lol

  • webmasterrip May 13, 2009

    Im not sure which relay it is that i should be looking at? Do you have any idea as the location the colors of the wires that are coming from this relay? i can run the test on the relay if you tell me what to do

  • webmasterrip May 13, 2009

    okay its the relay by the evaporator under the hood. I started the car and turned the a/c control from the off to max a/c position and it clicks everytime on and off. So doesnt that tell me the relay is switching? still no compressor operation. Another thing i left out is the plug for the a/c fell apart it had a small resistor in the plastic housing of the plug could that prevent it from coming on? I dont suspect that because like i said earlier if i apply 12 volts direct to the compressor the clutch engages and the system works.

  • webmasterrip May 13, 2009

    no im not sure if its a capacitor or a resistor this may be my problem how can i be sure? and do you know what power should be going into the relay i have a red, blue, orange , purple and black wire coming out of the relay

  • jjohnson505 May 19, 2009

    same problem here. 1991 corvette put direct 12v to compressor. works fine. last night replaced pressure cycling switch. finally found all existing 5 prong relays. tested all and they seem to be in good working order. few of them contacts are black but all five tested good. will be putting them back in tonight. but im sure the compressor will not be clicking on :( any ideas??


  • jjohnson505 May 19, 2009

    i understand if freon is low the compressor will not kick on. but if there is no power to compressor it also will not engauge.. what am i missing


  • Samuel Charles Spriggs May 11, 2010

    Testing the relay (I said this was involved):

    - remove relay

    - look at the schematic on the relay

    - determine which relay leads energize the coil

    - determine which relay leads are the switch contacts

    - apply 12 volt to the coil leads

    - put a multimeter on the switch leads (set to ohms)

    - if relay is good, you will get a 0-ohms reading thru the relay switch leads

    - if relay is bad, you'll get an infininte-ohms reading ("overload"), or you'll get a very high reading, like millions of ohms

  • Samuel Charles Spriggs May 11, 2010

    First, just because a relay is clicking doesn't mean it's closing an electrical circuit -- they almost always click -- this means the coil is working -- does not mean the contacts are good -- for relays to work, the coil/solenoid has to work, and the contacts have to be making good electrical contact.

    Secondly, yes, if there is a broken/loosely-connected resistor in the plug it will open the circuit and prevent current from going to the compressor. Are you sure it's a resistor, or maybe a capacitor?

  • Samuel Charles Spriggs May 11, 2010

    The relay should be very near the compressor. Wire colors, I have no idea. When the A/C is turned on the relay should click -- you will probably need someone inside the car turning the A/C on and off while you listen for the click.

    There couldn't be that many relays near the compressor -- do you see anything which looks like a relay?

  • Samuel Charles Spriggs May 11, 2010

    First, I don't think this A/C system is controlled by a computer.

    Since your info is in two postings, I'm getting kinda lost here.

    I think you mentioned a relay clicking. There is definitely a compressor relay. It could be that relay is faulty.

    Can you locate that relay? If you can, maybe try tapping it to see if it's stuck, and the tap will free it. If that doesn't work, it may be burned contacts in the relay. There is a way to test the relay, but it's very involved.

    If you don't want to test it, may be a good idea just to replace it.

    If you can do what I suggest, and get back to me, before you buy any parts, we can discuss next steps.


  • Samuel Charles Spriggs May 11, 2010

    I see you have reposted this problem -- neither of your postings is showing that this is a "paid problem". There is definitely a glitch somewhere -- it' s shown as a "free problem".

    If you'll work with us on this maybe we can find a solution -- paid or not.

    Sorry for the inconvenience.


  • Samuel Charles Spriggs May 11, 2010

    Well, if you jumped out the high pressure switch to get the compressor to run, it sounds like the high pressure switch is open because there is no pressure in the system.

    Have you checked the refrigerant charge?



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Posted on May 13, 2009


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Help I tryed this about 10 minutes ago i will give this one more try then im calling my credit card company. I have a 1991 corvette that has an a/c electrical problem the pressures are good the compressor...

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