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  1. #1
    Join Date
    Jan 2008
    Posts
    40

    Unhappy Heat pump problem

    Hi,

    I'm a homeowner with a heat pump problem. My service tech has been here twice, but he's not sure what it is. He checked the charge (it's fine). I'd really appreciate your input to help us diagnose the problem, since he doesn't want to just start replacing parts.

    Background: All-Carrier system (1997 vintage) with 2.5-ton heat pump, air handler and electric heat strips. The heat pump ran fine all winter. On Saturday I switched it to cooling for the first time this year. I noticed the following problem:

    - Heat pump starts normally and cools fine for the first 20 minutes or so (my tech checked the output temperature and said it was fine).

    - After running for about 20 minutes, a hissing noise can be heard from inside the heat pump (like refrigerant flowing in the lines, only louder). This noise gets progressively louder over a 10-minute period, until eventually it is quite loud and can be heard from 10 feet away above the fan and compressor noise. Along with this hissing noise, I noticed that the air blowing from the top of the heat pump, which is normally warm, gets progressively cooler until it is the same as the ambient temperature.

    - Eventually (after a total running time of about 30 minutes), the compressor and hissing noise both stop. The fan continues to run (since the thermostat is still calling for cooling).

    - At some point after that (say, a few hours - I'm not sure), the compressor restarts and the same cycle repeats again.

    That's it... To me, the hissing noise suggests some sort of gradual pressure build-up inside the heat pump, eventually causing the compressor safety mechanism to kick in. Trouble is, we're not sure what is causing the build-up. My tech said it might be the piston in the reversing valve gradually shifting due to a leak or crack in it, but he's not sure.

    Any ideas? We'd really appreciate your help on diagnosing this one.

    Thanks,
    cinergi

  2. #2
    Join Date
    Feb 2008
    Location
    Western NC
    Posts
    2,504
    yeah, you need a new technician

    Your compressor head pressure is through the roof. The compressor is going into overload. hence the hissing.

    Any good technician can diagnose and repair the problem. you need a tech that will spend the time on the system.....

    Not just take temps and gone 20 minutes later.
    I fully support the military and the War on Terrorism.


    If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.

    If you do know, then do. But do it right. Otherwise, you may not be doing it long.

  3. #3
    Join Date
    Jan 2008
    Posts
    40
    Well, in his defense, it was Sunday afternoon, so I suppose it was good that he came at all. He's supposed to come back tomorrow for a more thorough diagnosis - just thought I'd get a head start in case this is a common / easy problem. He's been very helpful with my other issues in the past.

    He did put his gauges on; the pressures were good when the unit was running OK, but he didn't stay long enough for the problem to occur.

    -cinergi

  4. #4
    Join Date
    Feb 2008
    Location
    Western NC
    Posts
    2,504
    There shouldn't be a "in his defense"

    Yes it is Sunday. I am on call. My phone rang at 530am. I got in the truck, drove 2 hours and spent 4 hours on the call.

    I cleaned and fixed an ice machine. They have an A/C down. Low on refrigerant. I performed a leak serch, found the leak, also found a bad expansion valve that needs to be replaced. I checked the compressor windings, checked the electrical and did a quick fix on the leak to prevent further contamination.

    I then called all the local suppliers after hours numbers and already have a new expansion valve on order. Gonna be here Tuesday.


    The fact that it is Sunday shouldn't mean anything to a technician that takes pride in his work. You called him, your probably paying good money for after hours service, and now he has to return to finish the diagnosis???? That seems a little off to me.
    I fully support the military and the War on Terrorism.


    If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.

    If you do know, then do. But do it right. Otherwise, you may not be doing it long.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,880
    So if you are taken to the hospital on a Sunday, and the ER blotches your care. Its ok because its Sunday.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  6. #6
    Join Date
    Jan 2008
    Posts
    40
    I agree with both of you that the problem must be diagnosed and fixed properly, and hopefully it will be. I simply meant that I called the tech at short notice, and by the time he got here (he was on another job at the time and had to finish that one first), it was already getting dark. He did not charge me for his visit, and said he would return to finish today. Although he said it might be the reversing valve, he didn't want to just replace it without confirming, which a less principled tech out to make a quick buck may have been inclined to do.

    Of course, you are both correct that the problem has to be diagnosed and fixed correctly. If he does, great; otherwise, I'll have someone else look at it. Does anyone know a good tech in the Montreal, Canada area?

    As for my original question, is there a common problem that could lead to the symptoms I described?

    Thanks,
    cinergi

  7. #7
    Join Date
    Aug 2001
    Location
    jackson,ms
    Posts
    15

    Hmm Trane to Amana

    Replaced 6-wire Trane heat pump with 5-wire Amana. Brown wire not connected. Auxiliary light on at Trane t-stat. Should I change t-stat to 5-wire?

  8. #8
    Join Date
    Jan 2008
    Posts
    40

    Update

    The TXV was replaced, lines nitrogen purged, system recharged, and a new filter drier installed. System runs great now.

    -cinergi

  9. #9
    Join Date
    Feb 2008
    Location
    Western NC
    Posts
    2,504
    glad to hear.

    Did he clean the coils while he was at it???
    I fully support the military and the War on Terrorism.


    If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.

    If you do know, then do. But do it right. Otherwise, you may not be doing it long.

  10. #10
    Join Date
    Jan 2008
    Posts
    40
    He cleaned the condenser coil. The evap was clean (I'm careful about my filter maintenance!)

    -cinergi

  11. #11
    Join Date
    Apr 2002
    Location
    Omaha, NE
    Posts
    1,561
    OK, guys. Here's what I don't understand: it sounds like the system was building up head pressure and eventually the internal relief valve was venting back to suction side. This would continue until the internal overload in the compressor would finally kick out. After cooling off awhile, it would reset. My question is this: how would a bad TXV cause this to happen? Why wouldn't it just pump down, and cut out on low suction pressure? Or just continue to run into a vacuum? Why the excess head pressure?

  12. #12
    Join Date
    Apr 2002
    Location
    Omaha, NE
    Posts
    1,561
    Or... is the TXV somehow sticking wide-open and causing the high head??

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