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  1. #1
    Join Date
    Jul 2005
    Posts
    26

    Hmm

    I went to check a unit today and there where alot of problems. the one that make me think the most about the unit is the fact that I went to pump the compressor down and when I got it pumped down i killed the power and watched the gauges. the low and high start to equalize and over about 20 min. the system had equalize. This is telling me that the valves are bad. Have not heard what the boss had told them but this is my first thoughs. Any ideas?
    Am I on the right track?

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,368
    Was it a heat pump?
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    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    Jul 2005
    Posts
    648
    Let the compressor run itself into a deep vacume. Kill power and wait 20 min or so. If the gauge moves, you have leaky valves, (given that your hoses don't leak, your gauge is accurate and it's done properly)

  4. #4
    Join Date
    Jul 2005
    Posts
    26

    Wink check that

    I pulled down as low as it would get it got to 30 psi and then the compressor shut off. It is a straight a\c not a heat pump. and my gauges are perfect. ( I say they are )

  5. #5

    Hmm

    So-o-o-o-o-o, what you are saying is that you tried to pump the refrigerant back into the condenser via the compressor, but at 30 psi the low pressure switch kicked the compressor out???? Was the line set/evap coil isolated from the condenser? If not, what kind of metering device is on the evap coil? With 30psi in suction side, eventually suction and liquid side will equalize through the metering device - unless you have a locked up TXV.

  6. #6
    Join Date
    Jul 2005
    Posts
    26

    results

    There is no pressure switch. The unit has a meter device and the system equalize rapidly.

  7. #7
    Join Date
    Jul 2005
    Posts
    26

    class room

    If i remember things correctly the valves should hold the refigerate longer.

  8. #8
    Join Date
    Sep 2004
    Location
    Portage
    Posts
    909
    Ummm. is this a scroll or recip. ?? or a heat pump like beenthere asked?

    [Edited by 1972torino on 07-25-2005 at 10:54 PM]
    I don’t always drink beer, but when I do I prefer Dos-Equis. I am the most interesting man in the world. Stay thirsty my friends.

  9. #9
    Ok-Ok-Ok. You pumped down to 30psi, and the compressor shut off - why did the compressor shut off?

  10. #10
    Join Date
    Jan 2004
    Posts
    144
    You said that there is a metering device. All systems have a metering device. The three most common are pistons (liquid line brazed to an adapter tube with a threaded coupling holding the piston inside), capillary tubes, and expansion valves. Pistons and cap tubes will allow refrigerant to equalize rapidly because they are simply calibrated restrictors in the line, TXVs will also allow equalization, but they vary the restriction based on superheat.
    You need to keep the compressor on until the suction pressure is 0 (I will not tell you how due to me not knowing if you will kill your self with high voltage or short out the control voltage circuit), then shut the suction and discharge service valves.
    Licensing laws are tough, and it's about time.

  11. #11
    Join Date
    Jul 2005
    Posts
    648
    Well I think I know what happened. Did you shut the liquid line service valve to pump the unit down? You may not have enough room in the condensor to pump the whole system down, depending on the length of the pipe run. Your compressor probably went off on either HP or LP. If your're checking compressor valves, jump out the LP temporarily to allow the compressor to run into a vacume. If the compressor is going off on HP, DO NOT JUMP IT OUT! You'll have to reclaim some of the refrigerant so that it will all fit in the condensor. See the problem with pumping most of these units down is that your only access to the high side of the system, is after the service valve. So you have no clue what the actual head pressure in the condensor is.

  12. #12
    Join Date
    May 2005
    Location
    toronto canada
    Posts
    25
    What made you decide to check the compressor valves in the first place?Why is the unit shutting off if there are no pressure controls?

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