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  • Automotive ac problem round 2

    I recently posted another thread about this. The background is that for many years I have had an ac leak which in some cases over a period of time but on occasion suddenly loses a certain amount of charge. The odd thing is that once that happens the system retains the rest of the charge.

    In any event I decided to fix this. I injected a UV dye and it looked like I could see some dye near a couple of fittings. In any event since I was taking the system apart I replaced all the seals, the schrader valves and the compressor shaft seal. Pulled a vacuum close to 30" Hg with a vacuum pump before recharging. After running it for about half an hour I turned off the pump and closed the valve and the system held the vacuum for almost an hour. On that basis I concluded that the system was leak free and recharged and everything was working well for several days with nice cold air.

    It has been cold recently so I dod not need ac until today. I turn the ac on and no cold air. Initially even the condenser fan was not running. After pulling out the relays it started working so I assumed it was a coincidental electrical problem. But still no cold air. I checked the compressor clutch coil resistance and the signal to it and it was fine.

    I then hooked up the manifold gauge set and it read 100psi high and 10psi low so guess what. It has lost charge again just like in the past and very suddenly. It possibly is on the threshold where the pressure switch may shut the system down due to low pressure.

    I'm now suspecting a faulty pressure release valve on the compressor. I will be jacking the car up later today to inspect to see if I can spot any oil around it which would confirm my theory.

    Other than this does anyone have any ideas what could cause an apparently sealed system to suddenly leak like this and how to I go about trying to track it down.

  • #2
    Re: Automotive ac problem round 2

    Sounds like a leak on the low side of the system. Most likely the evaporator coil.

    James

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    • #3
      Re: Automotive ac problem round 2

      Since posting this I got myself an electronic leak detector and sure enough the only place it keep alarming was at the cabin vents. I took the blower out to access the evaporator and it definitely was indicating a leak there. The alarm was especially loud in the lower right hand corner and when I inspected the area with my borescope I found evidence of damage - bent fins. I guessing maybe some object got pulled in by the fan and it hit the evaporator.

      In any event I have ordered a new evaporator - hopefully once installed that will be the end of this...

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      • #4
        Re: Automotive ac problem round 2

        I suggest pressurizing the system with nitrogen. I find it easier this way to find pesky little leaks.

        Interesting that you actually replaced a compressor seal other than r/r it. Not too many who do this.

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        • #5
          Re: Automotive ac problem round 2

          Good idea - I've heard about pressuring with nitrogen for testing. Not sure how you would find the leak though - soap solutions over the ac system? It seems easier to use a leak detector. But nitrogen would be a good way to check the system for leaks after repair since I've learnt that holding a vacuum does not mean the system will not leak when pressurized.

          Where does one get nitrogen for doing this.

          Yes I have a tendency to pull components apart and rebuild them myself. More interesting and you get to learn a bit more about the insides. I've rebuilt alternators and transmission valve bodies among other things.

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          • #6
            Re: Automotive ac problem round 2

            You can purchase Nitrogen from a HVAC wholesaler or welding supply.

            Be carefull not to go above the recommended test presure for the evap. coil. Auto evap. coils are made of very thinwall tubing.

            James

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