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A/C problems on '75 GMC

Discussion in 'Chevy Trucks' started by 75gmck25, Aug 20, 2003.

  1. 75gmck25

    75gmck25 Senior Member
    Messages: 119

    The compressor was missing from my truck ('75 GMC K25) when I got it and last September I got it working again by installing a rebuilt A6 compressor and various other parts (listed below). I also converted it to R134a and ester oil.

    It was working fine a couple of weeks ago, but this weekend I found the A/C did not work. The compressor clutch seems to engage (you can hear the engine RPM drop), but then it starts clicking/tapping from the vicinity of the A/C clutch. The clicking does not seem to disengage the clutch, since the engine stays loaded (rpm down) until I turn the A/C off again. The clicking almost sounds external (like the clutch), but could be coming from inside the compressor. The low pressure switch is still engaged when the compressor is clicking.

    I'm trying to figure out if the rebuilt compressor is already bad, or maybe its just the clutch or some other component.

    I haven't checked the pressures, since the place that evacuated and recharged it put some little heatshrink labels/locks over the fill valve covers. If the labels are removed it says it will void the warranty on their work. Its probably not a big deal, since all they did was leak check, evacuate and recharge.

    Bruce
    ------------------------------
    Work I did on the system last Septemer - took apart all connectors, put A/C cleaner through it and blew it clean with compressed air. Installed a rebuilt compressor, new accumulator, VOV, green O-rings and new hoses to the compressor. Added ester oil to the compressor and system. Had the system leak checked, evacuated and recharged with R134a.
     
  2. wyldman

    wyldman Member
    Messages: 3,265

    Is the compressor actually turning ? You should be able to see if the front of it is actually spinning,and not just the clutch slipping.It could be a bad clutch,or maybe the woodruff key has snapped off,and the clutch plate is just spinning on the compressor shaft.

    You should also be able to turn the compressor over by hand when the engine is off.You should be able to tell by how it feels if there is a problem.
     
  3. CARDOCTOR

    CARDOCTOR PlowSite.com Addict
    Messages: 1,310

    remove belt see if pulley will turn freely
    maybe bad clutch bearing





    cardoctor
     
  4. 75gmck25

    75gmck25 Senior Member
    Messages: 119

    Thanks for the suggestions. I've been out of town the last couple of days, but will have a chance to check it out tomorrow.

    I sure hope it turns out to be just the clutch. The rebuilt compressor is still under warranty, but I would need to have the system evacuated and recharged if I have to replace it.

    Bruce
     
  5. CARDOCTOR

    CARDOCTOR PlowSite.com Addict
    Messages: 1,310

    if it is the compressor
    make sure you have paper work for the other parts you replaced
    usually they wont warranty the compressor unless you have receipts showing the dryer and expansion tube were replaced




    cardoctor:yow!:
     
  6. 75gmck25

    75gmck25 Senior Member
    Messages: 119

    Thanks for the reminder. I found the receipt for the compressor, and it also lists the accumulator, new hose, and Ester oil. That should be enough for the warranty.

    As an update, I confirmed that the A/C clutch is engaging and turning the compressor. After listening more closely when the clutch is engaged, it sounds like the tapping noise I'm hearing is internal from the compressor.

    At this point I'm trying to decide if I should just bring it in to an A/C shop to have it checked (minimum of about $40), or pick up a cheap set of gauges and check it myself. I don't have any way to evacuate the R134a, or pull vacuum and recharge, so if I replace the compressor myself I'll still have to take it to an A/C shop twice. It was easier the first time, since the system was empty when I started.

    Thanks,

    Bruce
     
  7. wyldman

    wyldman Member
    Messages: 3,265

    I'd have it checked,as it may be over,or undercharged,or you may have too much oil in it.The compressor may actually be alright.

    If the compressor is under warranty,you may just want to start fresh,and replace it anyways.
     
  8. 75gmck25

    75gmck25 Senior Member
    Messages: 119

    An update to my A/C problems:
    I had the system checked today and they found that the compressor was working, but the system was apparently plugged somewhere. I had them recover the R134a, and when I opened it up I found that the orifice screen was plugged with a small amount of black grit. I had flushed the system before, but some of the grit must have been in the nooks and crannies of the evaporator or condenser.

    I couldn't find a place open that had another VOV (variable orifice), so I bought a Ford Blue orifice from Advance Auto. The blue orifice is smaller (.067) and it is supposed to give better performance than the stock GM white orifice (.072). I had it recharged and they put in 3 lbs of R134a, which is 80% of the 3 lb, 12 oz charge recommended for R12. When I got home I found a shop on the internet that suggested the GM A/C needs more like 3 lbs, 4 oz of R134a, so it might be a little undercharged. Current temps here are about 96 degrees, and the cab seems to cool down without any problem.

    Bruce
     
  9. wyldman

    wyldman Member
    Messages: 3,265

    Dirt will plug up any A\C system.Hope you got it all out.

    The blue Ford orifice tube is a well known trick on the GM trucks,and will work even on the newer ones.