a/c compressor knock

Discussion in 'General Chevy & GM Tech Questions' started by RATRODKING, Jul 3, 2011.


    RATRODKING Rockstar 100 Posts

    i have a 1990 k-1500 4x4 with 5.7 engine. a/c compressor about 18 months old. i hear a slight knock in the compressor when running the a/c. last night it seemed to get a little louder.
    is there a way to add oil to freon and have someone "top it off" with the freon/oil mixture, or can you only add oil before adding the freon ?
    thanks much.
  2. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    As far as i know the only way to add the oil is before you install it you put a measured amount of oil into the compressor. And if it is knocking then it is already starting to break apart.

    RATRODKING Rockstar 100 Posts

    thanks murdog..... yea, from what ive been searching, that sounds like it. i think i gotta replace the compressor.
    thanks again
  4. MightyMax

    MightyMax Rockstar 100 Posts

    You can buy a can of pressurized oil down at Adv. Auto or something and add it in like you would freeon.

    Did this on mine and I think it corrected my knock/noise.

    RATRODKING Rockstar 100 Posts

    today i had a brand new compressor, accumulator, orifice screen, oil and freon installed in my 1990 k-1500 4x4 with 5.7 v-8.
    its cooling fine, but i still notice somewhat of a slight nock when the compressor is turned on.....even increasing when i up the rpm's.....no where near as load as it was before he put the new compressor in..... is it normal for the compressor to make a slight knocking sound ? i dont have another vehicle to compare it to since i sold my 2003 s-10, but i dont think the s-10 ever made any knocking noise.... is the slight knock always present on these type of compressors in my 1990 ?
    thanks for the help guys.


  6. Chris Miller

    Chris Miller Rockstar 100 Posts

    I wouldn't worry too much if it's very slight. I've seen this more and more on aftermarket compressors. I put the one in my 94 suburban back in June of '08 and it's had a slight knock since day one, but it'll freeze you out of that truck still.

    RATRODKING Rockstar 100 Posts

    thanks chris, i appreciate it....

    RATRODKING Rockstar 100 Posts

    took the truck to the mechanic who fixed it 4 weeks ago. he said yes, the compressor is knocking more than it should be and will replace it free of charge.
    BUT he is gonna chase down a Delphi compressor and install it. he said they are hard to come by, for some reason.
    but it will be fixed soon....

  9. Ethan

    Ethan Rockstar 100 Posts

    You need to have the entire system flushed, sounds like crap from the AC system keeps getting sucked into the compressor and causing it to knock, compressors in these trucks have no knock, my 94 was retrofitted to R-134a a while back, and the original compressor is very quiet, no knock, but the entire system was rebuilt.

    RATRODKING Rockstar 100 Posts

    thanks ethan.... supposedly he does flush and vacuum the entire system out.. at least that is what he says he is doing..... hope to get it repaired this friday with the Delphi compressor.... its got a 1 year warranty, so if it keeps failing he will continue to get it back.

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