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Wish I knew WTH I was doing. Anyone want to help this old HVAC guy ?

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  • Wish I knew WTH I was doing. Anyone want to help this old HVAC guy ?

    Im a new user and would appreciate it if someone could help me understand what this cars ac system is telling me.

    This is a 2005 ford focus that belongs to my girlfriend. It was owned by her and her dad and he's since passed so there's no

    way she wants to part with the car. I just keep fixing everything that goes wrong with it. Its a money pit.

    The compressor went south last year so I decided to do a wholesale change out of everything I could easily get to
    other than the lines. I changed out the compressor / condenser / accumulator / RCD ( I don't know what the hell its called in a car. the restrictive device that goes inside the line, it was an orange one. this car does not have a TXV ) and all new seals anywhere I took anything apart that had seals.

    This car has always had a slow leak that I've never been able to find with the sniffer. Ive tried under the dash and the vents, the schrader valves, all connections and anywhere else I could think of. The sniffer never went off. I did test the sniffer with refrigerant and it works.

    Heres the crazy thing to me. I can pull it into 29in of vacuum and it holds overnight . Thats crazy considering that I know for a fact that there is a leak. Im thinking there is a leak somewhere on the high side while under operating pressure. At least twice a year I have to add refrigerant.

    So this time I pulled it into a vacuum for an hour and then let it sit for 30 mins to make sure it didn't drop. It didn't so I dropped some UV dye in and weighed the charge at 26oz per the Ford spec. The problem is that I have no idea what changes in the accumulator / condenser / compressor may or may not have been made by the aftermarket supplier. The dropped charge did not seem to be enough.

    According to the ambient T/P chart the car seems off on the published numbers. Thats not to say that those numbers are correct and are maybe just ball park numbers. I was an HVAC tech for 15 years but that was over 30 years ago in the days of ambient +30 for R22 systems. I know next to nothing about R134a auto systems. It just seems that the vent temp should be colder than it is. But maybe I'm wrong.

    Here are my numbers that I came up with that netted me the lowest vent temp.

    Ambient - 91.4

    Humidity - 75%

    AC control on max and blower on 3 of 4 with recirculate on.

    24" fan on high blowing directly into the grill of the car

    Car idling at 1000 RPM - Suction pressure 45 PSIG ----- High side 225 PSIG - vent temp with digital gauge and HVAC thermometer in vent - 63

    Car idling at 1800-2000 RPM - Suction pressure 30 PSIG -----High side 260 PSIG - Vent temp in vent 58

    At all times during this test, condensate was just pouring out of the drain and the accumulator was sweating.

    Are these numbers correct or do you think I have a high side restriction somewhere ? That restrictive metering device is what I would think could present a restriction.

    Any help would be appreciated.


    Heres the ambient T/P chart that I found online for R143a

    Also I have no idea if you should be looking at your pressures at idle or at 1800-2000 RPM.

    I have googled it and there seems to be no rock solid answer.

  • #2
    Forget that chart, it shows what someone thinks it should read.
    Temp/pressure chart for R12 and 134a are here:
    You might be slightly over charged, but I wouldn't worry about that right now.
    High ambient temp combined with high dew point (humidity) means it takes a lot of cooling just to squeeze the water out of the air.
    From the above chart you can see the frost point would be about 26 psi suction Your high speed high side of 260psi is aprox 148 deg condensing temp, or about 10 deg higher than I'd like to see as a maximum of 40 deg over ambient, which is why I suspect a slight over charge.
    A real common leak problem is the compressor shaft seal. Unlike a hermetically sealed compressor, the shaft seal has to seal with the shaft stationary as well as turning. It will see higher pressure with the compressor not in use than when it is running.
    If it leaks down and needs charging a lot, be sure to check and make sure you have enough compressor oil. as it leaks with the refrigerant. When in doubt, remove and drain the compressor of oil and re fill with the amount spec'ed.
    Try misting the condenser with water while observing the pressure and temps, If pressure and temp drop, and you know the condenser is good (cause you just changed it) then that would be another indication of an overcharge.
    Your system has a orifice tube (just a fixed restriction) and cycles the clutch to keep the suction pressure high enough to prevent iceing in the evaporator. (often around 28 psi). Right now pressure indicate it is not getting close to frost temp, part of that may be due to the high temp/humidity and part is because your condensing temp is too high.


    • #3
      ty for your input. I also need to make sure I dont have infiltration of heat from a out of sync blend door. I think im going to dump the charge and redrop it and see what happens. I took the car out for a drive and light to light city traffic is terrible. the compressor is shutting off. I can tell through the vent temp as soon as it shuts off. at highway speeds it seems to do as good as its going to do. it also shuts off under hard acceleration. what I dont know is if its shutting off on the low suction pressure switch or high head. i dont know how I would know other than running a set of gauges on the outside of the windshield.


      • #4
        Most cars, esp those with small engines, have a throttle cut-off switch that kill the compressor when high throttle setting (WOT) is called for.


        • bevis
          bevis commented
          Editing a comment
          Did not know that. that's an important bit of info. TY

      • #5
        Originally posted by bevis
        t. i dont know how I would know other than running a set of gauges on the outside of the windshield.
        Done that more than once, Put the hoses under the windshield wiper to hold it in place. It will answer some of your questions about what is shutting the compressor off.


        • bevis
          bevis commented
          Editing a comment
          if only ford didn't have a better idea. they put the damn low side access on the accumulator and stuffed it behind the front passenger wheel well. crazy.

      • #6
        A coupla years ago I found out that some mfg have a high pressure cut-out that varies depending on if the car is stationary or moving! Yep, different setting (higher for stationary) than moving. Guys car would cool at 100 deg sitting in driveway but would stop when he drove it. Only happened in real hot temps, Took leafing through the service manual I found on line to come across that little tid-bit buried in spec's.
        Car used to be simple with snap action switches to control things, now they use "pressure transducers" and a controller that reacts to a bunch of different inputs.
        Make my 30+ year old semi tractors seam like a dream to work on.


        • #7
          Damn, the hits just keep coming ... Hoping fix or repair daily is not one of those companies


          • #8
            Yeah, that one threw me until I was able to read the manual. I think it was a Nissan, and it was most defiantly a Tx valve system, so shouldn't have "cycled" the compressor like that.
            I never heard back if the guy got it solved or not, but from his pressure readings he was hitting the high pressure cut off limit.