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Thread: No cold A/C

  1. #1

    Default No cold A/C

    I just bought a 1991 Silverado. When I turn the AC on, air blows but it doesn't get cold. What's the first thing I should look at?

    p.s. the evaporator has a label on it saying "R12 and R134a compatible."

    Last edited by 80skeys; 03-27-2010 at 08:07 PM.

  2. #2
    Sr. Apprentice
    Join Date
    Nov 2009
    Grandview, WA


    Did you check to make sure the A/C Clutch engage when you turned the a/c on. Could also be low on Freon, take it to shop & they can pressure test for leaks. They can add dye to find any leaks.

  3. #3


    There does not appear to be an external clutch on the A/C compressor.

    There is, however a pair of wires. I decided to see if these were getting power. I used a test light. First with the A/C turned off and with it turned on. In both cases, no power. I figure this has got to be fixed before anything else. So I started tracing the wires (one dark green, one black) but they were quickly lost in a maze of wires towards the back of the engine compartment.

    Anyone know where to go from here? Is there a way to test the compressor using another source of power?

  4. #4
    Sr. Apprentice
    Join Date
    Nov 2009
    Grandview, WA


    The clutch is where the pulley rides on. Look at it when the engine is running without the A/C on & look at the pulley. The pulley will turn, but the inner part that is the clutch will not. But it all should turn with the a/c on.

  5. #5


    I recharged the system and brought the refrigerant pressure up within spec. Still no cold air.

    I also tested again the two electrical wires going to the compressor. Still no power.

    What's the next step?

  6. #6


    I went back a couple hours after putting refrigerant in the system to check the pressure. It's still holding at the same pressure it was when I added the refrigerant.

    On another discussion forum, they said try disconnecting the negative post on the battery, waiting a few minutes and then reconnecting to reset the computer. Did that, but it didn't help.

    Since the wires connecting to the AC compressor clutch are not getting power, should I try to "test" the compressor by jumping from another source of power?

  7. #7
    Master Mechanic bigdaddy77084's Avatar
    Join Date
    Jan 2010
    Houston, Texas, United States


    The wires carry juice to the magnets to kick it on and off. Run some wires to the battery & see what happens. It should turn on with the defrost on.
    95 tahoe 2dr 4x4 200,000+ miles

  8. #8
    Legend tlperry68's Avatar
    Join Date
    Oct 2008
    Huntington Beach, CA


    Quote Originally Posted by bigdaddy77084 View Post
    The wires carry juice to the magnets to kick it on and off. Run some wires to the battery & see what happens. It should turn on with the defrost on.
    Good idea.
    Trevor - Huntington Beach, CA
    2007 GMC 2500 4X4

  9. #9
    murdog94's Avatar
    Join Date
    Feb 2008
    Cloquet, Minnesota, United States
    Blog Entries


    Also put a jumper in your "low pressure Switch" it is located on the Dryer?? correct termiology?? Anyhow just run a jumper between the two contacts.. If the low pressue switch is bad you will just need to check the pressue periodically. I leave mine bypassed since i dont want to risk getting moisture into the system... Once you have jumped it fire up the truck and turn on your A/C.....
    Power will not be allowed thru the system since it is run in series thru the low pressue switch first... Just FYI....
    Note (the dryer is the part that is located on the firewall, and has the lines run to it)
    As much as i end up working on AC youd think id remeber.


    1997 Chevy S-10 Blazer 4X4 with 330K miles and counting (Hunting rig).

    2009 Saturn Aura XE (wifes car)

    2011 F-150 Crew 4X4

    "Hold it to the floor till you see God.... Then Brake!!!!"

  10. #10


    An update. I disconnected the low pressure switch and jumped the two wires together. I turn on the A/C switch in the dash and it causes the compressor to turn. I got a can of R-134 with a pressure gauge on it and hooked it up to the low side valve. I tried and tried adding refrigerant but it wasn't taking it. So I went to the store and got another can of R-134 - different brand with no gauge. I started the engine, turned on the A/C to get the compressor going, hooked this can up and it sucked it all in right away. Then I went into the cab and walah! I've got Cold Air now. This was yesterday and I drove around today and it's still working.

    I've decided to leave the low pressure disconnected, at least for while.

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