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Yet another home A/C problem

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  • Yet another home A/C problem

    The old R-22 system referenced in a recent thread worked great for a 4 or 5 days and quit again. It would start and run normally for less than a minute then the compressor & condenser fan would shut off.

    I let it rest a while, then hooked up the gauges and found that the low side would drop all the way down to 50 psi and then bam, the contactor popped open, shutting everything down. I noticed during the previous session that the charge port schrader valves were leaking and borrowed a nifty tool from a friend at work that allows you to replace the valves without discharging/recharging.

    I spent a big part of Fri trying to get the old valves out but they would back out a ways before squeeking to a stop. Fortunately I didn't listen to the friend who said just twist it harder because it would have just snapped off.

    I looked closer and found the brass fitting had been distorted from previous over-torquing of the dust caps and the schrader valves wer jamming on the way out. S-o-o-o, off to the lathe & mill I went to make a crude 6 flute reamer/cutter from drill rod with a hole drilled in the center to clear the valve tip. It worked a treat and I was finally able to change the valves succesfully. I then fired it up and added refrigerant until the low pressure was back up to the normal range.

    The suction line was the getting very cold all the way into the compressor and the pressures looked normal but after a few minutes it shut down again. I noticed the suction line coming out of the accumulator into the heat pump reversing valve felt warmer and the suction line from the reversing valve headed into the house was steadily warming up even though the pressure was OK and the line at the compressor was still very cold.

    So, I reckon the reversing valve must be sticking partially in the heat mode causing the compressor to overheat?? I tried cycling the rev/valve solenoid valve on & off rapidly by un-plugging & plugging the 24V wire while whacking the thing with a rubber mallet but got no joy.

    Anybody got any suggestions how to unstick the valve or do you think my diagnosis is correct? Fortunately the weather cooled drastically here yesterday but if I can't get it going I guess the time to replace the whole system has arrived.

    There's no way I can silver solder a new valve in, even if I could find one. There's just too many fittings in odd positions to try it. The other thing I thought about was to cut the whole mess out and solder in some pipe to bypass it and just run it as an a/c system but that looks pretty difficult as well.
    Milton

    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

  • #2
    I had a similar problem with my heatpump (Trane) a while back. If memory serves, it had something to do with the defrost control. It made it appear that the reversing valve was stuck.
    Mine has a motherboard with LEDs that flash for certain faults. Does yours have the same?
    Rich

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    • #3
      Thanks Rich. No, I haven't seen any led's on the board....it's a very old unit and has what looks like a diagnostic pin-out socket and I don't have a service manual for it.

      That's a good point you made about the defrost control....wish I knew more about how it works and what components to look at to take a stab at diagnosing it. Does the defrost cycle use the reversing valve to do its thing? The R/Valve solenoid looks like it is strictly an on/off device though and stays powered up the entire time the unit is in the cooling mode.
      Milton

      "Accuracy is the sum total of your compensating mistakes."

      "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

      Comment


      • #4
        The defrost cycle does use the reversing valve, which puts the unit in the cooling mode to warm up the outside coil. It's in one or the other position. There's no in-between if it's working properly.
        Any products mentioned in my posts have been endorsed by their manufacturer.

        Comment


        • #5
          First, a disclaimer: I am not a professional HVAC tech. I've installed heat pumps in some properties I own as well as in my shop. I do my own service work. But again, I am not a professional/certified/licensed tech.

          The reversing valve switches when the unit goes into defrost while operating in heat mode. Some units operate off a timer, others like the York unit in our house use a pressure switch to sense differential across the condenser coil. Reversing valves can and do stick or leak through, but if you are hearing a solid clunk when you activate/deactivate the coil, you can rule out sticking. You might want to do some reading on superheat and subcooling to better help you analyze the symptoms. There are some good pages on the Web that give comprehensive troubleshooting information. The HVAC forums will not be helpful to a DIYer.

          You are dealing with AC mode, and you probably know that gauge readings are useless when in heat mode. But, you will see a change in readings if the reversing valve does switch.

          I have fixed many pesky, slow refrigerant leaks by simply tightening the schrader cores a turn or so. My electronic refrigerant leak detector has been a tremendous time saver.

          If the unit is pretty old, you should give consideration to installing a new high efficiency unit. Last fall, I put one in a house that is all electric, built in the late 70's and not well insulated by today's standards. The tenant said her electric bills were about half that of the neighbors with similar houses. You could see a pretty quick return on your investment. I don't know if the tax credit is still in effect, but that would sweeten the pot more.

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          • #6
            Thanks! Yep, I've tightened the schrader valves several times but the seals finally died and had to be replaced.

            Looks like I don't have any defrost problems since there's a steady 24v to the solenoid, I think the internal shuttle piston is hanging partially open.

            I've just about given up on fixing it yet again and called a friend who is in the HVAC business to have him come by to give me a price on replacing the whole thing, inside & out. He says he doesn't like heat pumps at all but what else is there? I have a natural gas supply up to the house but a meter would have to be set and plumbing run up into the attic...expensive?? I thought electric heat is cheaper in this area than gas anyway and the new heat pumps were much better than before.

            I'll bet whatever I get won't be as reliable and repairable as this old York has been. It just turned 33 years old.

            Anybody have a recommendation as far as brand goes?
            Milton

            "Accuracy is the sum total of your compensating mistakes."

            "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

            Comment


            • #7
              Hate to hijack but DICKEYBIRD did sorta ask first:
              Does anyone know if installing a gas meter and the last 50' of gas line is expensive? In what kinda ballpark? Do you even have to buy the meter or does the gas company provide it? Be intrested to know if its like a $1,000 or $3,000 or $10,000 kinda job.
              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

              Comment


              • #8
                Originally posted by DICKEYBIRD
                I'll bet whatever I get won't be as reliable and repairable as this old York has been. It just turned 33 years old. Anybody have a recommendation as far as brand goes?
                You have mine beat. It was installed when I built the house in 1986. Reasonably dependable, the biggest repair I've made was when the top rusted out of the accumulator. A little paint would have saved me a lot of work.

                Like diesel pickups I suppose everyone has their favorite HVAC brand. I hear folks complain that the Yorks aren't as good as they used to be. That is what I put in the rental house last year, and I guess it is too early to say how reliable it is going to be. I put a Goodman split system in the new shop I built three years ago and have had no complaints about it so far. Cheaper than the York, and that is obvious in some respects. The most irritating thing is the timed defrost that cycles, IIRC, every 45 minutes. (Someday I'm going to look at modifying that.) But, it works for pennies a day, primarily because it has a 15 SEER and I went bonkers about making the 2000+ sq ft building well insulated and very air tight.

                I looked at the Professional HVAC forums before I bought the Goodman and it was really hard to find a consensus on which system really is best. When I replace the unit on the house, I suspect I will go with another York.

                Some people don't like heat pumps because they are used to the higher vent temps of fossil or resistance heat. But there are systems that produce much hotter air temps than before. Personally, I really can't see any reason not to like a heat pump.

                Comment


                • #9
                  If you have a source of cheap water, consider a water-source heat pump. It uses ground water as the heat source or heat sink. That's going to be a steady high-50s or low-60s degrees where you're located, so they're very efficient. The units are compact and extremely quiet. The one in my last house in SC was quieter than my refrigerator.

                  They can also be installed with a recirculating loop in the ground, but that adds a lot to the cost of installation.
                  Any products mentioned in my posts have been endorsed by their manufacturer.

                  Comment


                  • #10
                    Earlier in the week you had a question about the pressures on your system. I am going through A/C problems as well and came across this website so I thought I would share.

                    Regards,

                    http://toad.net/~jsmeenen/charge.html

                    Comment


                    • #11
                      A leaky schrader is annoying but with 1/4 " flare cap with copper gasket, it should not pass refrigerant to the atmosphere.
                      Does the indoor coil tend to frost up? If so either not enough R-22 or not enough air across coil.
                      There should be no reason for the unit to run a defrost cycle. ( on AC )
                      Your unit probably uses a TX valve for AC which does make it a little more difficult to get a proper charge.
                      I would sugest a good HVAC tech. root out your problem.
                      Jim

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