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AC troubleshooting help?

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  • AC troubleshooting help?

    I have an 07 Mustang that is having issues getting cold, mainly at idle. It seems like the system is just a bit tired. for starters, this is in Texas, so the ambient temperature when I took these measurements was 100 F. The ac does work, but maybe some refrigerant has leaked out. I'm a welder, not a mechanic so I don't have a lot of experience with ac systems. Anyway, here are the numbers:

    refrigerant: R134A

    According to Rockauto, this thing has an orifice tube and not a tx valve.

    pressures with the car not started:
    • Low Side: 110PSI
    • High Side: 110PSI
    Pressures with the car started:
    • Low Side: 25-45psi
    • High Side: 200-315psi
    comments about high side fluctuation: the high side pressure rises to 315, then the radiator fan kicks in, and the pressure drops to 200 and the fan kicks off and the pressure starts to rise again. During this time, the compressor is always engaged and never disengages. This leads me to believe that the condenser is not working as efficiently as it should be. when the high side pressure goes to 315 the low side drops.

    So, I sprayed the condenser with a garden hose while running, and it works pretty well according to my wife when I do that, it stays cold. The pressures when I do this are about 25psi on the low side and 160psi on the high side.

    This kind of makes me think the condenser needs a good cleaning, and there may be some moisture in the system, but I don't get the impression that the system is leaking. So, I was thinking of the following solution and wanted input from people who are smarter than me.
    1. get the system evacuated.
    2. remove the condenser and accumulator/drier.
    3. clean and straighten the fins on the condenser, and take some sort of mild solvent to clean the channels, maybe dawn, maybe someone has a recommendation. then probably dry it in the oven for a couple of hours on low. (I would really like some input on the best way to really clean the condenser because a new one is $588, Ultrasonic cleaning? I knew of a guy that blew systems out with nitrogen. I have argon/co2 mix, idk)
    4. Replace the accumulator/drier.
    5. pull a vacuum for a couple of hours and see if it holds for 24 hours.
    6. fill by weight to spec.
    It seems like nothing is broken in the system; it just sucks. The compressor seems like it was compressing fine, and everything seems like it was working electrically, so plugged-up cores are the only thing I can think of with a combination of high ambient temperature. Is this too much, or should I do more? I'm not against pulling the evaporator out and cleaning it and replacing the orifice tube tool and every seal, but I really don't want to throw $1300 in parts at the thing. I have more time than cash, and I'm in no rush because this is my wife's "project" (I don't know why she wanted a 07). I would appreciate any input.

  • #2
    Your pressures are in the ball park so I don't think you have a leak. The high side (condensing temp) seams to be the problem.
    315 is 163 deg F or there about. 200 is 130 deg F or there abouts.
    IF and this is an IF the air passing through the condenser is in fact 100 deg F, 130 deg condensing temp is about all you can expect from the condenser. That would be 30 degs above the air passing through it. No air cooled condenser is going to to get much better than that.
    25 psi on the low side is right at freezing, so that is good. Problem is when the condensing temp rises with the fan off, you aren't loosing enough heat at the condenser and it gets recycled to the evaporator, with a corresponding rise in temp/pressure.
    Your compressor not cycling is as it should be when the evaporator pressure/temp is above freezing. In short the system is working flat out and struggling.
    I don't think you are going to see much change even if you put a brand new condenser in, the drop in pressure when the fan kicks on, shows only a 30 deg difference between the air temp and the refrigerant condensing temp.
    Your statement "
    Originally posted by whyIsitSoHot
    It seems like nothing is broken in the system; it just suck
    is spot on.
    Anything you can do to increase airflow over the condenser will help, but the fact the fan(s) aren't on until pressure is up in the 300 psi range, is the issue.
    Getting that hot before turning on the fans will be less noticeable when the air is cooler, but the hotter it gets, the less room for extra heat there is in the system.
    In short: I don't think there is anything that is going to make the system marked better. Spending money on tearing it apart and putting back together only to end up back where you started isn't helpful. I think the system is operating as designed, may be not as needed, but it is doing all it can.


    • #3
      P.S. 110 psi at rest shows 93-94 deg F so a little cooler than 100 but not much. Your still in the ball park with 35 deg spread on the condenser. Running on hot blacktop the air through the grill may well be higher than 94 or even 100 on a sunny day.


      • #4
        I think I'd explore to get all the electric fans operating whenever the AC is switched on.

        Originally posted by Cornbinder89
        Running on hot blacktop the air through the grill may well be higher than 94 or even 100 on a sunny day.
        I'm in Arizona, and temperatures a couple of feet over the blacktop could be way hotter than 100F, likely 130-140F !!! Today should be 114F in Phoenix.


        • #5
          Texas? 800 miles X 800 miles is huge but is making news of the 100+F temps for most of it!

          Add it's the highest sunlight of the year surfaces bake, heat rises and that's what your vehicle is dealing with.

          It does all those temps in New England just short times out of a day or if working over usually "blacktop/asphalt" vs concrete the short time of checking anything varies 50F is impossible to be credible info adding engine heat just futile.

          What others may do I can't know but I don't know a single shop that uses A/C for indoor working areas - zero.

          Stuck - need to know before that best you can. My own exact area to work/check is full sun is too hot for me to be there sorry come back another if the vehicle runs OK without and driver can take it or seek alternative transportation.

          Since this is so widespread bet renting something is scarce. Stuff happens, can't help that,
          MetroWest, Boston