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  1. #1

    Hmm High Suction Low Head

    Hey guys, I have a compressor doing something I have not seen before. Granted I have only been in the field for 5 years

    I have a York split system with a scroll compressor. Two TXV and no hot gas bypass.

    The unit was not cooling well, 67 deg leaving air temp. I checked the pressures and had a 90 suction pressure and only 225 head pressure. My outdoor temp was a lil over 90deg. Superheat was 40 and subcool was 15. Amp draw was running at the listed fla of 9.5.

    Im in Louisiana and this unit was working fine before the hurricane. A day after the power was restored to the building the unit starts going nuts. I did add some gas to the system to see if my head pressure would come up. It did eventually but by the time I got it up t 275 the compressor went out on internal overload.

    I also checked my TXVs both were slightly sweating on the leaving side of the TXV going into the evap coil.

    ATM I am thinking I have a compressor problem. I dunno, I'm not used to seeing high suction and low head pressures.

  2. #2
    Join Date
    Aug 2008
    Location
    Philadelphia
    Posts
    84
    is this a newer scroll compressor? newer scrolls will "unload" via bypass if the head is high. it sounds like you might have a dirty condenser (maybe not visibly) or non-condensibles left over form an earlier, less discriminating, technician.

  3. #3
    Join Date
    Aug 2008
    Posts
    131
    Is it a 3 phase unit?? If so Try to reverse the phase and see what happens.

  4. #4
    Join Date
    Sep 2008
    Location
    Delaware
    Posts
    243
    Two possabilities that jump out to me! You said that everything was fine until the storm, correct? What changed? My guess is you lost power and things got hot.
    So on restart you could be overloading the machine and lifting an internal relief or bypass, or the phasing of the power may have gotten changed causing the unit to run in reverse. Your discription sounds like either one but I would go for the reversed rotation first as it is easy to determine.

  5. #5
    I bet it is a phase problem, I will try that and see what happens, thx guys.

  6. #6
    Quote Originally Posted by DeepSouth View Post
    I bet it is a phase problem, I will try that and see what happens, thx guys.
    A 3 phase scroll will only pump one direction in my experience.

  7. #7
    Join Date
    Jul 2008
    Location
    hearth planet
    Posts
    87
    hi i'm working on a chiller doing the same thing, it was working ok but after a heavy storm it went nuts, high suction pres. 95 psig and head pres. 215 psig. changed txv and it's working fine.
    another one did the same, had a leak and still a clear sight glass, fixed the leak add some refrigerant and that was it.

  8. #8
    Well, it was not a phase problem. I spoke with a guy who has been in the biz for over 30 years and he told me that his guys had seen a few like this. They ended up changing compressors and that solved the problem. He thinks it might be cause by a bad check valve type device in the compressor.

    I took the bulbs lose on both TXV to make sure they were not sticking but I did find out that the evap is 10 seer while the condenser is 13 seer, giving me another problem to work out.

    Forget CSI. I think old A/C men make the best detectives

  9. #9
    Join Date
    Sep 2008
    Location
    Delaware
    Posts
    243
    A scroll will pump in both directions (why not?) but properly only in one direction. When running backwards they are not moving the proper amount of refrigerant as evidenced by high BP, low HP, low amp draw, and shutting down on winding stat due to insufficient motor cooling. The low ref. mass flow can also impact lubrication of bearings.

  10. #10
    Join Date
    Sep 2008
    Location
    arlington, tx
    Posts
    225
    where are you checking superheat and subcooling?

  11. #11
    Checked it at the condenser

  12. #12
    Join Date
    Jun 2006
    Location
    midwest
    Posts
    126
    Add a little reefer and watch for gauge fluctuations in opposite directions. Most likely a restriction in the TXV causing the low suction-high head.

  13. #13
    Join Date
    Sep 2008
    Location
    arlington, tx
    Posts
    225
    where does the line set run does it have good insulation maybe your pickin up alot of superheat from the environment i know its an annoying problem but with that much subcooling dont add any more gas you may want to try turning the valve counterclockwise and see what happens

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