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  1. #1
    Join Date
    May 2010
    Location
    Las Vegas
    Posts
    54

    Heat Pump Tripping on High Head in Heating

    Greetings,

    I am working on a R22 Lennox Split Heat Pump 3 ton. The unit will trip on the compressor relief valve in heating. I was unable to test the unit S/C and S/H accurately, due to the High Side pressure building up so fast with in a minuet will be hitting 400psi and blow the low side would sit at about 50psi. I tested the RVR from cooling to heating, and even tested the unit in cooling for a bit, pressures were ok. When in cooling my high side was 135 and low 50psi with an outdoor temp of 45degres and indoor temp of 75 degrees. I then switch back to heating and the same problem would occur. I have good air flow and in cooling the spilt seemed to be acceptable. The only other issue to mention, was when I arrived the customer stated that this summer they had a service company repair a pin hole leak somewhere in the system. I looked all over the coil, could not see any repair, or where they made the repair. I also did not see a new filter dryer installed, only the old one still in the system. I am puzzled the unit seems ok in cooling, the SH in cooling about 8 degrees, could the RV be not setting all the way in heating, or is there an issue with the TXV, with the possibility of recent sealed system work, I have a concern that there may be a restriction.

    Any Ideas? Happy New Year

  2. #2
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,051
    You gotta pull some juice out and see what she runs like then.

    You can see if the outdoor txv is working once you get it running steadily.

    You may have a partial restriction or other charge issue leading to overcharge in cooling

    Pretty common. IMO.

  3. #3
    Join Date
    Jul 2007
    Location
    Phoenix, AZ
    Posts
    206
    Sounds like a bad outdoor txv valve which is causing a restriction. Check the outdoor txv sensing bulb cap tube. Cap tube may have lost its charge. Look for crack or rubbed through spot somewhere on the small tube. Or just the txv is bad its self. You may have to dump some charge to keep it running to figure out where the restriction is.

  4. #4
    Join Date
    Nov 2012
    Location
    Tahlequah OK
    Posts
    131
    When the head pressure goes up during heat mode but is okay in the cooling mode and it rises as fast as you say the problem will have to be a blocked liquid line dryer or a TXV problem. You should be able to see a frost line at some point unless it is a total blockage. Are you sure you have good air flow across the indoor coil? What about the strip heaters? Are they on the down stream side of the coil?
    Last edited by welling service; 01-01-2013 at 08:54 PM. Reason: add a thought

  5. #5
    Join Date
    Apr 2012
    Location
    Cleveland
    Posts
    611
    Maybe the leak repair was adding that leak stop stuff and that caused a restriction.

  6. #6
    Join Date
    Jun 2011
    Location
    Seattle WA
    Posts
    1,245
    Quote Originally Posted by welling service View Post
    When the head pressure goes up during heat mode but is okay in the cooling mode and it rises as fast as you say the problem will have to be a blocked liquid line dryer or a TXV problem. You should be able to see a frost line at some point unless it is a total blockage. Are you sure you have good air flow across the indoor coil? What about the strip heaters? Are they on the down stream side of the coil?
    If its a blocked line dryer wouldn't the suction side pump down in cooling?
    America; first we fight for our freedom,
    then we make laws to take it away.

    -Alfred E Newman

  7. #7
    Join Date
    Jul 2012
    Location
    Dillwyn, VA
    Posts
    44
    Check the Discharge line temp outside the outdoor unit. If extremely hot like in the 200's the outdoor TXV is bad. I had a armstrong unit do the same thing. Run fine in cooling but in heat i had normal suction pressure head pressure pegged out and very very hot discharge. Changed TXV and unit running Ok

  8. #8
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,051
    This kind of shotgun diagnosis can get you in trouble.

  9. #9
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,038
    Was the indoor coil replaced? You said they repaired a pin hole leak but could not find where they did the work. Maybe they put in the wrong size of indoor coil.

    Next thing I'd look at is the indoor TXV. If it's not bypassing you could see what you are seeing.
    Beware of advice given by some guy on the Internet.

  10. #10
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,038
    Was the indoor coil replaced? You said they repaired a pin hole leak but could not find where they did the work. Maybe they put in the wrong size of indoor coil.

    Next thing I'd look at is the indoor TXV. If it's not bypassing you could see what you are seeing.
    Beware of advice given by some guy on the Internet.

  11. #11
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,861
    Quote Originally Posted by SBKold View Post
    You gotta pull some juice out and see what she runs like then.

    You can see if the outdoor txv is working once you get it running steadily.

    You may have a partial restriction or other charge issue leading to overcharge in cooling
    Pretty common. IMO.
    x2
    We really need change now

  12. #12
    Join Date
    Jul 2012
    Location
    Dillwyn, VA
    Posts
    44
    The outdoor TXV is stuck open, you can try putting the bulb in ice water to see if TXV closes and also putting the bulb in hot water to see if it opens. Watch your suction pressure. You need to check airflow, you should be moving 1400 cfm. Put unit in emergency heat mode and check temp rise. You should have around 34 degree rise for 15 kw heat strip or 22 degree rise for 10 kw.

  13. #13
    Join Date
    Nov 2011
    Location
    USA
    Posts
    405
    Quote Originally Posted by SBKold View Post
    You gotta pull some juice out and see what she runs like then.
    I would agree with that. The 50 psi saturated temp is about right for 45˚ OD. The summer repair probably ended up with an overcharge.

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