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Thread: A/C Recharging issues

  1. #1
    Is it a Mazda or a Subaru KrayzieFox's Avatar

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    A/C Recharging issues

    So I had to evacuate my A/C to remove the evaporator unit in order to fix a nasty water leak I had behind the dash on the passenger side (cracked body seam). That job is all done, but now I'm struggling with getting the A/C recharged.

    I rented a vacuum pump and gauge kit from AutoZone, and bought several cans of R134a refrigerant. I'm trying to follow the service manual and countless YouTube videos that demonstrate this, but the refrigerant simply won't go in. I'm hoping someone here has done this and might know what's going on.

    Here are my steps:
    1. Pull vacuum on entire system for an hour
    2. Vacuum holds at -29 inHg for well over an hour
    3. Charge 300g (~1 can) through the High port (as suggested by service manual). A little goes in on its own, but warming up the can in a bucket of warm water helps get the rest of the can in.

    Now this is where I get stuck. The service manual says to charge the system halfway (300g) through the High port with the engine off, then charge the rest through the Low port with the engine and A/C on. The 300g I charge through the High port enable the compressor clutch to engage and click on, but no refrigerant gets drawn in through the Low port. It's almost like there's a valve somewhere blocking the flow...

    Something in the evaporator unit? Thats the only part of the system I had to take out for this project. I've tried this a couple times now and no matter what I do, nothing goes in through the Low side.

  2. #2
    Certified Mazda Tech hornsfan10609's Avatar

    2003.5 Mazdaspeed Protege x2

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    I have had the valve on top of the freon can prevent the freon from entering the system, once I backed it off some the system started charging. I have never seen anything that recommends charging on the high side. I don't see any reason why the system will not take freon once the compressor is cycling unless there is a blockage on the low side, which would show very high pressures on the low side.

    I am no AC expert by any means, but I have used the vacuum pump/freon can/gauge setup method to charge AC and replace compressors in my garage in the past with success.
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  3. #3
    Is it a Mazda or a Subaru KrayzieFox's Avatar

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    I thought it was strange too, but that's straight from the service manual. Here are a few snapshots.

    And I'm definitely getting flow from the can since I can get some to go into the high side. But when I open the low side valve the pressure just hangs out at ~70 psi, which is definitely high for the Low side.

    My guess is that the heat expansion valve in the evaporator is closed, but I have no idea how to get it to open.
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  4. #4
    Certified Mazda Tech hornsfan10609's Avatar

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    The system could be clogged or a line bent to prevent freon from going in the system. Is the system at 70psi no matter if the car is on or off?
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  5. #5
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    I would bet that there is a problem with your low side service port. You aren't getting flow from your gauges to the low side of the system. The 70psi is pressure from the can.

    I had that problem once too, forgot to tighten the low side connector so it didn't push in the Schrader valve. Doh!

    You can charge through either side initially. However once the pressure in the system equals the pressure in the can, no more freon will enter. At this point you need the compressor to engage and draw the low side pressure down lower than the can, so freon will enter the system again and you can continue charging.

    With the compressor running, you should never attempt to charge through the high side, the can may burst.
    Last edited by MrGiggles; 09-13-2017 at 09:50 AM.

  6. #6
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    protege5

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    You may have a stuck expansion valve as well. This would be my first thought. Either that or a restriction somewhere, but since your AC compressor didn't implode on itself this isn't too likely. Many times when an AC compressor eats itself up it will send trash all throughout the lines and you have to flush them or guaranteed to get crap stuck somewhere it doesn't belong and cause AC issues.

    How long was the system left open to the atmosphere? did you change the dryer? Any time you open the system it is wise to replace the dryer, the desiccant sucks up any moisture pretty much immediately.

    I'd still put my money on the expansion valve. I'll replace one every time i touch an evaporator whether it needs one or not. They're cheap and many times just exposing them to the atmosphere seems to cause them to not operate correctly, especially on a car that's 15 years old.

  7. #7
    Is it a Mazda or a Subaru KrayzieFox's Avatar

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    The expansion valve seems to be the culprit here, there's just no flow from the low side. The Low gauge never moves, it just hangs at the pressure of the can, around 70 psi as mentioned.

    The compressor clicks on and the High side rises slowly to around 110 psi, and that's where it stops.

    Should I pick up a used evaporator from a junkyard? Do I have to go with a new one? Or should I just replace the expansion valve?

  8. #8
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    You'd think if the valve was stuck there would be very high high side pressure. Did you make sure the low side service port is clear and working?

    You don't need to replace the evaporator. In my case the fittings were a real pain to get apart, but I replaced the evaporator without replacing the expansion valve.
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  9. #9
    ......................... i12drivemyMP5's Avatar
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    Wouldn't you have to short the thing that prevents compressor from running when low on refrigerant so that it'll run and suck in the new stuff? Had to on my old Toyota truck. Haven't messed with it on the P5..........

  10. #10
    手前の言葉が俺は聞き捨てよう TheMAN's Avatar


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    Yes, that's what mechanics do, rather than trying to fill it up on the high side with the A/C off (as the manual says)
    The only time the high side is used is with an A/C refrigerant machine, with the A/C off
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  11. #11
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    I've never had to do that. Charged dozens, with and without a vacuum.

    Also depends on the low side switch cutoff, but normally it only takes 20 or 30 psi to trip it.

  12. #12
    Is it a Mazda or a Subaru KrayzieFox's Avatar

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    The ports are clear and gas is able to flow, I've verified that multiple times.

    And I don't think I need to short the compressor because I followed the manual by charging half way through the high pressure port with the engine off. This was enough to trigger the compressor to come on.

    My problem seems to be that the low side pressure simply doesn't change. It hangs at whatever pressure the refrigerant canister is at. The high will bump up to around 110 psi max after the compressor runs a bit, but after cooling off the high side equalizes with the low side.

    Anyone have any insight into what's going on here?

    Edwin, I see you're still around here after all these years. I seem to remember you knowing everything about these cars.

    What's broken? Where did I go wrong?
    Last edited by KrayzieFox; 09-19-2017 at 02:43 AM.

  13. #13
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    If that is truly the case, you either have a stuck expansion valve, or the compressor is spanked. The latter would be unlikely considering that it worked fine before you took it apart.
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  14. #14
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    protege5

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    Replace the expansion valve. This is exactly why i replace it every time i open the system whether it needs it or not Save the time of doing the job twice!

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