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Thread: 86 A/C Enigma

  1. #1

    Default 86 A/C Enigma

    So I read many threads and thought I found the issue. Apparently not. Forum User Error I am sure ;-)

    My A/C compressor does not engage. I pulled the A/C Cutoff Switch/Relay and jumped the red power wire to the black/green compressor wire and the compressor engaged. Problem identified! (or so I thought). Replaced the relay with a new one, compressor still won't engage.

    Did I chase the wrong part? Or did I get a rare "bum" one from the supplier?

    Any advice greatly appreciated.

  2. #2
    FEP Super Member
    Join Date
    May 2003
    Roseburg Oregon


    Are you sure the system has a full charge ?
    clowns to the left of me , Jokers to the right

  3. #3


    Good question. I was told when I bought it that it had been charged, but that it needed a switch. So that was the reason I acted on the cutoff switch. Now that I look into this further perhaps he meant the low-pressure switch? Not sure that is a DIY item if it is possibly under pressure? Can it be tested somehow, or is that a shop item?

    Thanks for replying, appreciate it

  4. #4
    FEP Power Member vintageracer's Avatar
    Join Date
    Sep 2008


    Low pressure switch on the accumulator screws on and off easily for replacement with the system under pressure.

    FIRST thing you need to do is to confirm that the system is STILL properly/fully charged and NOT leaking.

    Based upon your comments from the seller you are taking their word that the system was charged properly and still is charged properly. IF you find the system is low on Freon "I" suggest you open the system, replace the accumulator, orifice tube and all 10-12 system rubber O rings and then recharge the system.

    Low system gas pressure = LEAK!
    Last edited by vintageracer; 07-12-2018 at 11:30 AM.
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  5. #5
    FEP Power Member
    Join Date
    Nov 2007
    San Mateo, CA


    Quote Originally Posted by vintageracer View Post
    Low pressure switch on the accumulator screws on and off easily for replacement with the system under

    Low system gas pressure = LEAK!
    Since you have some info that it was maybe ok, You can jumper the switch to see if that engages the compressor. Don’t run it long. There are 2 types of switches. One for R12 and one for R134.
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  6. #6


    Thanks Vintageracer and Kevin, appreciate the info. I will check that out and go from there.

  7. #7


    I had a similar issue with mine. you might check the wire that supplies power to the low pressure switch. On mine it never did. I traced it back to the switch in the dash and found the wire between the A/c switch in the dash and the low pressure switch was broken. So I spliced in a new wire from switch in dash to low pressure switch. works great.
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  8. #8


    Thanks Moosh. I actually jumped the wires and although it runs the compressor, it blows warm. I figured I would have it checked out, but my mechanic and the local A/C shop are both swamped with the hot weather. So I figured I would simply by a can at O'Reilys and see what's what on the pressure.

    Turns out the fitting is different on the compressor when compared to the refill can. It would appear this 86 is still plumbed for R12, not the newer R134. At least that is what I am told based on the fitting and no "sticker on the compressor" that stated otherwise. Apparently you cannot get R12 easily unless you find a shop that has some left and then it is expensive.

    Anyone out there still running R12? Any suggestions on how one goes about converting to the new stuff? Does it require swapping out components?

  9. #9

  10. #10


    Thanks Swearint.

    So the entire system needs to be replaced? Wow, I was thinking new fittings, maybe a hose. Looks like a project for winter.

    Thanks again

  11. #11
    FEP Super Member
    Join Date
    May 2003
    Roseburg Oregon


    That lmr thing is not entirely true .
    I have done this procedure many times , and had satisfactory results .
    Go to O'Rileys , rent a vacuum pump .
    Harbor freight and buy a set of manifold gauges .
    Evacuate the system .
    If it holds a vacuum great .
    Install the conversion 134a fittings , they screw right to the R12 fittings .
    Fill with the 2lbs of 134a .
    The a/c will work until you have the money to replace the dryer and o ri gs with the green o rings for 134a .
    Some will scream this won't work , but I can tell you it works fine .
    clowns to the left of me , Jokers to the right

  12. #12


    It’s not hard to convert an R12 system to 134a

    There is an Esther oil that is compatible with both. Comes in the mcparts store conversion kits

    purge the R12 via reclaimer if there is any left.

    thread the 134a adapters on the high side and low side fittings

    the R12 pressure switch works fine with R134a — for most peoples purposes anyway. It runs the system at slightly lower pressure than the 134a loves but it cools plenty good enough in any foxbody — for sure if it has tinted windows even when down south. My 89 convertible didn’t and on triple digit days it was still plenty cold enough. Within about 10 degrees of what it was with R12 and that’s without changing most of the system

    On the cars that went away from thread on fittings at the condenser the O rings usually wear out. Buy spring lock clamps to keep them from moving around.

    For purging the air out of the system once it’s assembled a lot of guys prefer and the books all recommend an evacuation.

    Me personally I do it the way the old timers did it before this evacuation BS was thought up. They would do an air displacement. Basically you hook on to the low side and leave the AC off. Depress the sharder valve on the high side and start giving it 134a with leak detection dye until you start seeing more than trace amounts of dye coming out the high side. Then close the high side and engage the AC compressor.

    you get around 1/4 lb more R134a into the system that way than you will sucking it down one atmosphere then filling. Blows about 5 degrees colder doing the displacement based method in my experience — so VERY near R12 results without the R12 drama or the need for tools most people don’t have

    Good luck with yours

  13. #13


    Great advice guys, will give it a shot. Will at least buy a little time...

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