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Need Help- High Pressure on Discharge Side

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  • Need Help- High Pressure on Discharge Side

    Hello All,

    I'm looking for some help and advice on my a/c system. I am trying to get the a/c going on my '69 Mercury Cougar. It is a factory system. When I got the car I noticed someone had done some work on the a/c system. It had a newer condenser, receiver/drier, and 2 of the 3 hoses were replaced. I pulled a vacuum on it, got down to 27 inches of vacuum, I waited for an hour and it held so I charged it. I noticed the compressor making some noise so I shut it off, hooked up my high side gauge, restarted the car and noticed when taking the engine slightly off idle the high side pressure would quickly climb to 400psi.

    I took the whole system apart, cleaned all of the components individually, except the compressor with a pressurized flushing agent, replaced the receiver/drier, removed the compressor, drained the oil in it and refilled the system with fresh oil. I pulled a vacuum, it held so I proceeded to charge, still got the same result with high pressures on the high side.

    Before charging I left the discharge hose off and blew compressed shop air into the hose it came out of the service port I left open on the suction side. I thought the "quick disconnect" might be suspicious also

    Anyone have any ideas on what could be the problem or what I need to check?

  • #2
    ? '69 Cougar. OMG Numerous engine choices and possible set ups for so called "factory" A/C set up might not be? Should have used back seating service ports like this so need to know...…

    Testing memory pls bear with me. Those are 1/4" reverse threaded to operate with hope the picture shows. If not in the correct position to "operate" the system will block off the suction or discharge side and in the middle can vacuum and observe pressures. These if OE all had sight glasses on R/D or in line takes guesswork out if using R-12?

    Last edited by Tom Greenleaf; 07-25-2018, 01:04 AM.
    MetroWest, Boston


    • #3
      Hi Tom, my car was originally a 351 2 barrel, vin code H. You are spot on with the service valves, I actually replaced them and that is the diagram that came with them. I wind them all the way out when I'm not servicing the system or needing a gauge reading. Some one "custom" made new hoses for my car and there is no sight glass anymore.


      • #4
        My 1984 Jeep Cherokee had manual service valves like that, I loved those. One morning Mrs. Cusser had the compressor seize on the way to work, belt stalled the engine. I went there and cut off the damaged belt. This was early 1990s, and new compressor for it was like $600-$700 so I went to a Jeep parts yard on other side of town and they removed a compressor from a wrecked Cherokee, got it for $75. The theory is that "all vehicles in Arizona have working AC" like yesterday's 116F so I closed the service valves, removed compressor, and bolted in the used one. On that Cherokee the drier required radiator removal, so I didn't touch that, just bolted in the used compressor, added 6 oz. R-12, and AC worked fine until we sold it in 1994....

        I used a 1/4 inch drive socket turned around and used an allen wrench to open/close those valves.


        • #5
          That's the cool part about those valves is you can isolate the compressor so you don't lose all of your refrigerant when servicing the compressor. That is how the factory manual said to check the oil level in the compressor.


          • #6
            Those were great. Just the compressor was a bit busy sounding on those did well though for the few I knew even some in non automotive applications so nice to isolate a unit.
            Side note: You can get an 8 point socket if the square is good and NOT round the stem all up. OE they came with an aluminum cap also sealed over that stem. If missing I'd find some somewhere I think they were all the same?
            MetroWest, Boston


            • #7
              I still have the factory aluminum caps and my replacement valves came with plastic caps so I'm covered on them I have just been using a 1/4 open end wrench to open and close, but thought about using a socket


              • #8
                ? Never smashed one open but think those seal metal to metal should be firm when closed (if needed or wide open to run) positions - no leaks please. Try the fit of a 1/4 drive socket or extension the square end and mess up that. Open end is asking for trouble IMO hate to see you reduced to vice grips over wrecking those,
                MetroWest, Boston


                • #9
                  Yeah probably not a bad idea to switch to a socket to keep from chewing them up because I definitely don't want to have to use vice grips on them.. thanks for the advice!


                  • Tom Greenleaf
                    Tom Greenleaf commented
                    Editing a comment
                    Yes - It was a yacht with two A/C systems one always needed a boost early in the season was rounded a bit scary huge boat no chance to do even find a leak it wasn't fast and too much going on all over the place. Anyhow used a socket backwards as I recall OR the extension for !/4 then the 8 point you can get anywhere is for square plugs, odd stuff vehicle or otherwise just don't get screw up (no pun) over the thing! Tom

                • #10
                  Do you have any in and out temps at the condenser? Have you had the expansion valve out and apart? Sounds like you either have a blockage or very high heat. CHeck your temperatures all around, after you check the screen in the Tx valve.
                  Tight Lines!