Results 1 to 6 of 6
  1. #1
    Join Date
    Mar 2007
    Posts
    26

    Lennox Heat Pump Roof Top Unit.

    I have a Lennox Heat Pump Roof Top Unit giving me problems. Model#CHP20-653-1Y Serial#5696L02192. I is tripping out my high head pressure switch on high discharge pressure. The head pressure switch is set to trip out at 410PSI. This seems to be happening in the heat mode when my reversing valve not energized. This switch is located on the discharge side of the refrigeration circuit before the reversing valve. I have monitored the discharge pressure on the unit up to an hour and a half and it hold steady at 280PSI and will climb up to 320PSI when I bring in my auxilary/emergency heat but, that is it, no more than that. This unit is tied in to a energy recovery unit using 100% outside air. I have checked the filters and the belts and everything is fine. Direct Driven Blower motor in the Lennox unit works of some ice cube relay's. The only way I can get the high head pressure switch to trip is when I disconnect my blower motor. Any suggestions? It seems to happen when I am not at the site in the heating mode.

  2. #2
    Join Date
    Jan 2003
    Location
    Kansas City
    Posts
    1,482
    I am not sure why your high side pressure would increase when the aux heat was energized as the strips should be after coil, but high pressure trips are usually caused by low airflow over the indoor coil and system refrigerant overcharge. Look for possible changes in airflow due to dampers or recovery ventilators. Check the refrigerant charge and compare to manufacturers specs. I would expect to see about 5 deg subcooling in the cooling mode if the specs are not available. I have had to relocate some high pressure switches from the discharge line to the liquid line due to nuisance trips on cooling units, but I would expect that to have been an ongoing problem if that was it.

  3. #3
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,024
    I think there is a mild ambient kit for these units.

    It cycles the outside fan motor. This lowers the suction, and in turn lowers the head.

    I'll look for some information.
    Beware of advice given by some guy on the Internet.

  4. #4
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,024
    I can't find the info. I had a CHP16 that would do about the same thing, but never fixed it. Lost account due to some BS
    Beware of advice given by some guy on the Internet.

  5. #5
    Join Date
    Mar 2007
    Posts
    26

    Unit fixed.

    This problem is fixed. Something I failed to mention is that they had recently changed out thermostats at the site. It turns out that the configuration on the thermostats was causing this problem, let me explain. There are (4) Heat-pump rooftops at this site. Only one unit was working correctly with the new thermostats. The only unit that was working correctly with the new Honeywell thermostats was Lennox heat pump unit M# CHP20H-311-1P. The unit's that were giving me problems where the Lennox Heat Pump M# CHP20-653-1Y models. If you print out both wiring schematics and you will see how selecting the O setting in the configuration mode does not effect anything on the CHP20H-311-1P wiring schematic and how it makes a big difference on the CHP20-653-1Y. Having power to the W1 terminal at all times will bring on the refrigeration cycle and back feed voltage to my blower fan and run the heating cycle all the time making the space to hot till the head pressure switch trips. The fix was selecting the B setting in the configuration mode so it only send power to the W1 terminal on the call for heat. I was unable to attach a soft copy of the wire schematics. This could easily cause a lot of headaches on many install of with this type of equipment.

  6. #6
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,440
    Barfield Air Systems,

    This is the Ask Our Pro's forum. In order to post advice here, you must have verified qualifications and have been approved by the AOP Committee.

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