• Login is located in the upper right corner of all pages.


No announcement yet.

Flushing an Automotive AC System

  • Time
  • Show
Clear All
new posts

  • 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; 10-14-2020, 03:47 PM.


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


      • #4
        Originally posted by Cusser
        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
            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.


              • #8
                I've put about 50 hours of use on the AC system and today it may be on it's way out again.
                Today I think I can hear the compressor just beginning to "moan" when engaged.

                That moaning, if it is the AC compressor....means that my flush and recharge has failed.

                The next step is to remove the belt and see if I feel any resistance when turning the compressor.
                Obviously, if the compressor is failing (again) then running it any further will just introduce more and more metal shavings into the system.

                Not sure what went wrong this time....maybe too much residue remained from the denatured alcohol flush?
                Maybe the system had more shavings from the last compressor failure and I was not able to completely remove it all and it has begun circulating in the system?

                Maybe I didn't add quite the proper amount of oil? since I have a microscope, I may take a sample of the fluid and exam it closely to see if it was debris such as metal shavings.

                Not sure.

                My only recourse is to go back to the junk yard and get yet another compressor ($35.00)

                Quite a bit of work.

                I'm thinking about replacing the Condenser this time. They are available for this vehicle for about $55 (Chinese)

                Bummer....but what are you gonna do?
                Take it to a shop and pay $1000 ??


                • #9
                  Cleaning a system with known debris is always iffy and a judgement call on how much you clean, what you replace, do you install a filter and how do you deal with that if it clogs?
                  Don't fret until you KNOW what the problem is. With generic multi pass condensers so cheap, it don't re use any that I have a questions about.


                  • #10
                    It's possible the noise may not have been the AC

                    During install, I estimate I may have lost an ounce of oil because it spilled from the compressor during installation.

                    Today I added 2 oz of PAG 46 low viscosity oil to the compressor just to be sure it wasn't low since being over a little is less harmful than being low of oil.

                    in any event, I've driven the car around today with the air on and no problems. Compressor sounds normal. Will check pressures soon.

                    Cornbinder, you advice was good. (Don't fret until you know what it is) Thanks.


                    • #11
                      Video of the gauges and specifications for this vehicle

                      Obviously, the gauges show that the Freon charge is low.

                      I've decided to leave it LOW since that means less stress on the compressor and the temperature in the cabin is adequately Cool.
                      Last edited by King-of-DIY; 10-23-2020, 03:31 PM.


                      • #12
                        Without knowing the the temp of the air passing thru the condenser, you can't say it is low. Pressures tell you what is happening, not what the charge amount is.


                        • #13
                          Originally posted by Cornbinder89
                          Without knowing the the temp of the air passing thru the condenser, you can't say it is low. Pressures tell you what is happening, not what the charge amount is.
                          My apologies.
                          The ambient air temperature during that test was 84F

                          I attempted to give that information in the beginning of the video.
                          Perhaps I didn't make it clear.

                          Would you agree that given the ambient air temp of 84F, the gauges did indeed indicate a low freon condition?
                          Last edited by King-of-DIY; 10-23-2020, 11:51 PM.


                          • #14
                            Pressures can't tell amount of charge, they can infer a low charge but can't be used as an absolute measure of charge. What they can tell is the temp at the measured point of the refrigerant if the system is run long enough to stabilize pressures.
                            What I see is high side showing a condensing temp of between 110 and 115 deg, or about 30 deg over ambient. The low side shows a evaporating temp that quickly drops to near freezing then drops off after that, then the system cuts out. It might be low on charge, or it might have a restricted Tx valve. pressures alone can't tell the difference.
                            The condensing temp is in the ball park of where it should be. Anything over 40 deg over ambient is bad, the closer you can get it to ambient the better. In other words, the more heat you can shed at the condenser the better.
                            If not enough liquid refrigerant makes it into the evaporator, then it will all boil to gas long before it reaches the outlet. and the low side pressure will be low. WHY not enough refrigerant is making it into the evaporator, is not something a gauge can tell.
                            250PSI @ 85 deg F is roughly 147 deg condensing temp! That is lousy heat rejection by the system almost 65 degs over the air temp passing over the condenser. With all that heat remaining in the system there is no way you'll have good cooling.
                            "performance charts" show what someone thinks the system "should" be doing. Pressures show what the system IS doing. I don't put much stock in performance charts!


                            • #15
                              Excellent !

                              I will no doubt need to read this numerous times.


                              • #16
                                AC is still working fine.
                                I guess the noise is expanding freon rather than a compressor noise.
                                After opening the hood and listening to the compressor, it sounds smooth and quiet.

                                This was an experiment in flushing the AC system with denatured alcohol rather than expensive store bought flushing agents.
                                At this point I would call it a success and will go this route again in the future.

                                A GALLON of denatured alcohol was $20 and did the heavy lifting in removing metal and other debris in the system.
                                I used ONE quart of commercial flush compound after the denatured alcohol flush.

                                If you are a DIY person, please don't forget to flush your new evaporator core, like I did this time.
                                Save yourwself tons of headache.


                                • #17
                                  Almost 10 months later.....

                                  AC still working fine. Nice and Cold in the car and today it was 95F outside.


                                  • #18
                                    IDK how I missed all that even 10 months worth? Anyway if it's now worked especially on a used compressor and didn't see a "condenser" mentioned as new it's hard to argue anything now. Good luck for it to last a good long time for you,
                                    MetroWest, Boston


                                    • #19
                                      Originally posted by Tom Greenleaf
                                      IDK how I missed all that even 10 months worth? Anyway if it's now worked especially on a used compressor and didn't see a "condenser" mentioned as new it's hard to argue anything now. Good luck for it to last a good long time for you,
                                      Thanks Tom.
                                      I was mostly concerned with using a substitute for very expensive flushing chemicals.

                                      Apparently it worked. I did not change the condenser.
                                      Used compressor I just pulled off another vehicle at U-Pull-It junk yard.

                                      If the time comes I need to open the system again I will probably change the condenser just to be safe. It's very cold now, but still not "quite" as cold as a new car system.
                                      But cold enough to make the inside of a Dodge Caravan chilly on a 95 degree day.

                                      Thanks for the positive reply.


                                      • #20
                                        It works is the end game for this. Reason for tossing condensers is they are such fine paths and clog or anything shutting down one end you can lose more than just what got plugged - debris from compressors is the reason.

                                        Used is scary but did and would. Look for a right one still in the car see by clues it was working, has pressure and not out in the weeds for long. Read inspection stickers and know a ton about it.

                                        All worked! That was a lot of work to find a non front end wreck.

                                        Chems etc the costs are nasty IDK how to help that. Compressed air for some stuff at high volume. Make sure what you use is dry and not still in it of course. IDK how that would mess up but it wouldn't be working long if things weren't right,

                                        MetroWest, Boston