Page 2 of 3 FirstFirst 123 LastLast
Results 14 to 26 of 28
  1. #14
    Quote Originally Posted by atcherservice View Post
    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
    I would check 2 things. You mentioned a new filter drier. If it is a liquid line filter drier, is it a biflow?(being it is a heat pump the drier must be a biflow drier) if it is a suction line drier, is it installed between the suction line and the reversing valve?(this is the only place a suction line drier can work in a H.P). Usually on Lennox the liquid line drier is right before the txv and I have seen people add a liquid line drier on the outside of the service valves and leave the factory drier installed. I have seen that cause enough restriction to cause problems but doesn't really sound like the problem. If you have a biflow liquid line drier and it is pumping down and tripping high head pressure in heating but not A/C mode your ourside TXV is bad. The TXV is locked up and will not open to allow refrigerant to the outside coil resulting in low suction pressure and high head pressure causing the compressor overload to trip or a discharge stat to open. I would replace the TXV but at the same time take the drier out of the factory location(right before the TXV) put in piece of 3/8 copper pipe where the drier used to be and put a new biflow drier on the outside of the service valve of the unit so that in the future if the drier ever needs to be changed you can pump the refrigerant into the condenser and change the drier without reclaiming.

  2. #15
    Join Date
    Nov 2008
    Location
    baltimore
    Posts
    26
    Correct me if I am wrong, but if txv on outdoor unit were bad. Would you not pump down the low side due the outdoor coil acting as evap coil. Since this is happening so quickly I would look at rvr, airflow at indoor ahu, indoor coil, indoor txv (make sure flowing thru in heat).

  3. #16
    Quote Originally Posted by terpfan_ View Post
    Correct me if I am wrong, but if txv on outdoor unit were bad. Would you not pump down the low side due the outdoor coil acting as evap coil. Since this is happening so quickly I would look at rvr, airflow at indoor ahu, indoor coil, indoor txv (make sure flowing thru in heat).
    If your txv is bad on the outdoor unit your suction pressure is in the outdoor coil and the txv starves the coil and your suction pressure will pump down just as if the indoor txv where to lock up in cooling. Your head pressure is not going to raise the levels that they are as quickly as they are with a mis-sized coil. If your reversing valve is bleeding your suction will normally raise and head with fall as you are dumping discharge gas into your suction line(will act like a discharge bypass). If your fan is not on it may jump that high but I assumed from the post the fan is running. If the system has an indoor txv for A/C you would not pass discharge gas through the indoor coil(the condensing coil in heating) in turn your head pressure would not be high if you are checking on the liquid line because you have not passed gas thru the condenser.

  4. #17
    Join Date
    Nov 2008
    Location
    baltimore
    Posts
    26
    Quote Originally Posted by Branderson0515 View Post
    If your txv is bad on the outdoor unit your suction pressure is in the outdoor coil and the txv starves the coil and your suction pressure will pump down just as if the indoor txv where to lock up in cooling. Your head pressure is not going to raise the levels that they are as quickly as they are with a mis-sized coil. If your reversing valve is bleeding your suction will normally raise and head with fall as you are dumping discharge gas into your suction line(will act like a discharge bypass). If your fan is not on it may jump that high but I assumed from the post the fan is running. If the system has an indoor txv for A/C you would not pass discharge gas through the indoor coil(the condensing coil in heating) in turn your head pressure would not be high if you are checking on the liquid line because you have not passed gas thru the condenser.
    I agree a drier could cause this problem. I am confused in your statement about indoor coil txv not allowing hot gas thru it. This is precisely what it does in heat pump mode, usually at about 80%. The poster never said where he had his gauges hooked up. If you hooked gauges up on cooling suction and liquid line ports, a pressure drop across indoor coil could be seen. This would help eliminate the indoor section. If outdoor txv was only allowing partial flow and the system were overcharged I could see high head.

  5. #18
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,032
    Quote Originally Posted by Branderson0515 View Post
    If your txv is bad on the outdoor unit your suction pressure is in the outdoor coil and the txv starves the coil and your suction pressure will pump down just as if the indoor txv where to lock up in cooling. Your head pressure is not going to raise the levels that they are as quickly as they are with a mis-sized coil. If your reversing valve is bleeding your suction will normally raise and head with fall as you are dumping discharge gas into your suction line(will act like a discharge bypass). If your fan is not on it may jump that high but I assumed from the post the fan is running. If the system has an indoor txv for A/C you would not pass discharge gas through the indoor coil(the condensing coil in heating) in turn your head pressure would not be high if you are checking on the liquid line because you have not passed gas thru the condenser.
    The head pressure will sky rocket with an undersized coil on a Lennox heat pump. The only way to match an indoor coil with a Lennox heat pump is with the engineering data.
    Beware of advice given by some guy on the Internet.

  6. #19
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,032
    An indoor txv not bypassing in heat mode will cause a high head pressure condition. It becomes a discharge gas restriction.
    Beware of advice given by some guy on the Internet.

  7. #20
    Join Date
    Jan 2010
    Location
    Vancouver Island
    Posts
    342
    Quote Originally Posted by Milk man View Post
    An indoor txv not bypassing in heat mode will cause a high head pressure condition. It becomes a discharge gas restriction.
    This makes sense. OP should check TXV and make sure it is correct for a heat pump. Needs to have the reversing check valve or a bypass circuit with a seperate check valve.

    Sent from my SGH-I747M using Tapatalk 2

  8. #21
    Join Date
    Nov 2011
    Location
    USA
    Posts
    377
    Quote Originally Posted by Milk man View Post
    An indoor txv not bypassing in heat mode will cause a high head pressure condition. It becomes a discharge gas restriction.
    I disagree. The indoor TXV is at the outlet of the coil in heat mode, so it would be a liquid restriction. But based on the given information,

    low side would sit at about 50psi.
    ..there is no restriction, or very little, since the suction pressure is somewhere near normal for the OD temp.

  9. #22
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,032
    Quote Originally Posted by Saturatedpsi View Post
    I disagree. The indoor TXV is at the outlet of the coil in heat mode, so it would be a liquid restriction. But based on the given information,



    ..there is no restriction, or very little, since the suction pressure is somewhere near normal for the OD temp.
    I agree, but disagree. It the indoor TXV is not bypassing, partially or fully, it will back the liquid refrigerant into the indoor coil. As the liquid stacks in the coil there is less area for the discharge gas to condense. This will cause the head pressure to spike.

    It takes less refrigerant in heat mode than cool mode. The excess refrigerant is usually stored in the accumulator in most units, or the properly sized indoor coil in a Lennox. Now the coil essentially smaller and hot gas is being continually add until the HPS opens.
    Beware of advice given by some guy on the Internet.

  10. #23
    Join Date
    Nov 2012
    Location
    Tahlequah OK
    Posts
    131
    Not necessarily. it is a bi-directional dryer and could be blocked in one direction.
    Quote Originally Posted by LibertyTree View Post
    If its a blocked line dryer wouldn't the suction side pump down in cooling?

  11. #24
    Join Date
    Nov 2011
    Location
    USA
    Posts
    377
    Quote Originally Posted by Milk man View Post
    It the indoor TXV is not bypassing, partially or fully, it will back the liquid refrigerant into the indoor coil. As the liquid stacks in the coil there is less area for the discharge gas to condense.

    This will cause the head pressure to spike.
    That's what happens with any liquid line restriction, regardless the location of the restriction. But, the restriction alone, won't cause the head pressure to increase. That's due to something else.

  12. #25
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,032
    Quote Originally Posted by Saturatedpsi View Post
    That's what happens with any liquid line restriction, regardless the location of the restriction. But, the restriction alone, won't cause the head pressure to increase. That's due to something else.
    In straight cool units a liquid restriction, in most cases, will not cause high head pressure. The liquid will simply stack in the outdoor coil. Since it's a closed system the refrigerant is being pumped from the low side and not being replace. Run out of refrigerant on the low side and nothing will be added to the high side.

    In a heat pump the liquid will stack in the indoor coil which is smaller than
    the out door coil. The indoor coil will run out of room to store the liquid refrigerant. Plus if it's the indoor TXV causing the restriction, the liquid line will also not be able to store refrigerant like in the cooling mode.

    Furthermore, the refrigerant that is being stored in the accumulator, the outdoor coil, and liquid line is being pumped as a hot gas into the vapor line and liquid filled indoor coil. This by all purposes now a discharge gas restriction. There is no place for the discharge gas to go. The head pressure will skyrocket.

    I've seen this in the field before. Amana RTG36. Head pressure skyrockets. I replace the indoor TXV and solved the problem. I did nothing else to the system.
    Beware of advice given by some guy on the Internet.

  13. #26
    Join Date
    Nov 2011
    Location
    USA
    Posts
    377
    Quote Originally Posted by Milk man View Post

    I've seen this in the field before. Amana RTG36. Head pressure skyrockets. I replace the indoor TXV and solved the problem. I did nothing else to the system.
    I've never seen it, but also never seen that particular issue. And I'm sure there's a lot of other things I've never seen...I certainly won't argue with someone who has.

Page 2 of 3 FirstFirst 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event