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Flushing an Automotive AC System

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  • Flushing an Automotive AC System

    First post.

    I am currently working on a 2006 Dodge Caravan AC system
    Apparently, a new Evap was installed but not flushed and had significant contaminants in it that subsequently ruined the compressor in short time.

    At this point I have the AC system completely disassembled and I am flushing the system.
    I am using a loaner tool to do this that I got from AutoZone.

    The "fly" in the ointment is the flushing fluid.

    At auto parts stores, AC flush is approximately $22 for ONE QUART.
    In my opinion it is not possible to adequately flush an automotive AC system that is known to have contaminants in it such as metal shavings and or
    sand grit. I find that AT LEAST a gallon is needed to properly flush everything. That would be over $100 for enough flush to clean the system properly.

    Obviously, car repair shops often have machines that run fluid through the system automatically and monitor the contaminant level.
    that is ideal....but I do not possess such a machine nor have access to one and I'm not paying to have it done.
    So I must adequately flush the system with the resources I have.

    What I just did is bought a gallon of denatured alcohol and used that to do the major flush, and then I will follow that with a light flush using the expensive AC flush fluid.
    BTW, LOTS of contaminant did come out. I caught some of the flush as it exited the system and I found lots of metal particles along with some grit.

    When an automotive AC compressor fails, that often puts quite a bit of debris in the system. The filter dryer might catch somet of it DEPENDING on where the debris originates
    and whether the dryer is a filter dryer or just a dryer.

    For example, if you install a new Evap core without cleaning it and it contains manufacturing debris such as grit from sandblasting, that will go directly to the compressor.
    The Filter/dryer/receiver is AFTER the compressor. So ALWAYS clean new Evaporator cores before installing them.

    Some dryers are not designed to do filtering, but simply to remove moisture from the compressed liquid leaving the compressor.

    I have yet to see how this flush with denatured alcohol works out. I have read many success stories.
    denatured alcohol is said to leave a residue. That is why I'm opting to run just ONE quart of regular AC flush through the system
    after the denatured alcohol.

    That said.....one quart is not really enough to flush an evap core and a condenser coil.
    So this after flush is mostly to help remove the film that might exist from the denatured alcohol.

    In any event, I'll mark this forum and try to remember to report back a year from now on how it did.

    I'm not exactly asking a question....but feel free to comment.

  • #2

    Finished flushing.
    I flushed the condenser twice with denatured alcohol and once with store bought AC flush.
    I flushed the replacement compressor.
    I flushed the evap core (expansion valve removed) with denatured alcohol, then a final flush with store bought AC flush.
    I flushed ALL the hoses.

    On the final flush I sampled the expelled fluid from both the condenser and evap coils.
    To the naked eye and bare skin, the results seem good. No more noticeable contaminants as had been noticed before.

    Note that I reverse flushed the condenser, forcing the flush fluid into the upper, outlet and letting it exit the liquid line

    At this point I'm using compressed air to dry out the coils before I begin re assembly.

    I find that a considerable amount of flush fluid can remain trapped in the bowels of the coils.
    So I'm spending a good bit of time blowing them out.
    I won't stop until I see no mist and no droplets at the outlets.

    I'm using ND-8 (PAG 46) oil as recommended by the factory manual.

    The compressor came from a junkyard car but passed my junkyard on-site tests.......
    1). looks reasonably good
    2). There is at least some pressure still in the AC lines when disconnected
    3). the inner shaft tuns easily with no noticeable resistance or noises.
    4). If I cover the suction outlet with my thumb, I can feel some suction being developed as I turn the center shaft.
    5). No visible contaminants in the compressor upon visual inspection
    6). The car looked as though it had been under air (no mildew, rot, sagging headliners etc)

    Hoping for a good outcome as I need to make a 1400 mile road trip with it.
    Last edited by King-of-DIY; 6 days ago.


    • #3
      If that condenser is parallel flow type, then flushing/reverse flushing won't go through any clogged passages.


      • #4
        Originally posted by Cusser View Post
        If that condenser is parallel flow type, then flushing/reverse flushing won't go through any clogged passages.
        The one thing that makes me think it worked is that some debris did come out during the flush.
        I suppose if there are too many clogged passages i won't get very cold air and it could soon ruin the replacement compressor.
        I'm rolling the dice and taking my chances.

        At risk is the dryer and compressor.....about $60 worth of parts.

        HOPING I won't need a new condenser. But ya never know.


        • #5
          My plan is to add the entire 6.1oz oil charge directly into the compressor and then install it.

          Is that a bad idea?


          • #6
            Originally posted by King-of-DIY View Post
            My plan is to add the entire 6.1oz oil charge directly into the compressor and then install it.

            Is that a bad idea?
            No, not a bad idea at all. Connect the line fittings and then rotate the compressor drive plate (the inner part) about 10 times with a wrench to move the oil mostly out of the compressor; compressors compress gases, not liquids.


            • #7
              After overcoming all obstacles, I have cold AC again.
              I did have considerable trouble getting the hoses at the compressor to seal, but after getting a new set of nitrite and metal gaskets it seems to be sealed now.
              I think using Denatured Alcohol was a good and economical idea. A final flush with regular AC flush hopefully removed any possible harmful residue.

              I think I will go the denatured alcohol route again in the future.
              It was about $25 for a gallon and it did remove considerable metal particles and grit from the system.

              I was able to flush the evap and condenser multiple times....until the flush was clean.

              Now it will take time to see how it goes. Remember, I plucked the compressor off a junk yard vehicle for $35
              Fortunately there seems to be no seal leaks and it obviously makes good pressure. Luck....plus a defined set of inspection rules.

              I'm by no means an expert......so if I can do it, you can do it.