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Lennox Heat Pump "Mystery" issue.

nipri
nipri Member Posts: 3
in A-C, Heat Pumps & Refrigeration

I'm calling this a mystery because I currently have 2 contractors baffled by it.

In heat mode, the outdoor unit will run perfectly well for some number of days before shutting down, as if someone actually removed power from it (no compressor, fan or any other activity)

The indoor unit continues to run and push hot air, heated from the electric backup heater strips.

The only way to recover the outdoor unit is to power cycle the system from the breaker box. When I do that, the thermostat "heat on" indicator flashes as if the compressor had been short cycled. After about 5 minutes, the outdoor unit starts and runs normally until the next go around.

Refrigerant charge is normal. I was told that tis could happen with excessive head pressure caused by a clogged air filter but ran the system with no air filter and then a new one, replaced about 1 month ago.

Had the outdoor unit services about 8 months ago to replace the condenser fan and compressor starting cap. This problem preceded this repair and continues to this day.

Air conditioning mode is flawless.

All ideas appreciated!

Comments

  • ratio
    ratio Member Posts: 3,852

    Do the calls go away at the heat pump (i.e. no 24VAC between Y and C & O and C)? That would indict the thermostat.

    If the heat strips are on, did the HP call for them (energize W/W1/whatever)? Maybe there's a low ambient lockout thermostat that's shutting down the HP & passing the heating calls back to the heat strips; or the defrost board is getting stuck.

    Lots of different things could be going on, just going to have to catch it while it's happening.

    bjohnhy
  • yellowdog
    yellowdog Member Posts: 230

    Thermostat issue? It goes into second stage but will not come out of it. Does the thermostat ever satisfy while its only running on the electric elements? If it doesn't satisfy, it sounds like the second stage is not large enough or you have a wiring issue. New problem? Or only since it got real cold?

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 17,006

    I would suspect a defrost issue. maybe a bad defrost board

  • nipri
    nipri Member Posts: 3

    Just replaced the Tstat, will see if that makes a difference. Next is to get someone to pull the cover on the outdoor unit while in this fault state to see if the defrost board or controller board is flashing any codes.

  • yellowdog
    yellowdog Member Posts: 230

    2 "contractors" are baffled by this and nobody has checked for codes yet?

    mattmia2
  • pecmsg
    pecmsg Member Posts: 5,598

    Has the refrigerant charged be recovered and weighed?

    Has the static pressure been checked?

  • mattmia2
    mattmia2 Member Posts: 11,354
    https://forum.heatinghelp.com/discussion/comment/1837360#Comment_1837360

    I think there are a lot of basic steps that have been missed here before opening the sealed system. Like reading the theory of operation in the manual and seeing what is asking for what.

  • pecmsg
    pecmsg Member Posts: 5,598
    edited January 23

    refrigerant charge is normal

    in 50 years of during refrigeration, I’ve never seen normal listed in the manuals

    Super Heat

    Subcooling

    Weighing the initial charge

    Wasn’t that system open to initially charge it?
    I agree don’t jump gauging up. But during heating season, the only way to know is to recover and weigh the charge.

  • nipri
    nipri Member Posts: 3
    edited January 23

    The last error code indicated a bad defrost board which was replaced about 2 years ago. It could be bad again.

    New thermostat installed and static pressure / charge checked OK yesterday. I had service done on the system yesterday because I lost aux heat (one of the strips had opened… there are 2 5 KW strips in the system that satisfy the thermostat which I usually keep set to 68 deg. The outdoor unit was actually shut down in failure mode yesterday morning however, given that the outdoor temp was -8F and indoor temp was dropping through the 50s, I had to recover the outdoor unit to get whatever little heat I could while waiting for someone to come out.

    Once the new strips (on order) are installed and I have decent heat again, I can afford to leave the outdoor unit in its failed state while someone comes to inspect it.

    Just to note, this system is appx 10 years old and is on it's 3rd evaporator coil. I'm more that ready to s**tcan the entire system. Planning to sell the house soon though so am torn between replacing it and sinking yet more money into it.

    Like i said above, the defrost board was replaced about 2 years ago and this problem has been ongoing since at least then. That 3rd Ecoil was replaced about 1 year ago. About 1 week after replacing that 3rd coil, the outdoor unit acted up again. I was told that the air filter was clogged causing the unit to go off on high pressure but the problem continued after replacing the filter (the guy did a 2500.00 repair job on the indoor unit and didn't check the filter?)

  • pecmsg
    pecmsg Member Posts: 5,598

    Multiple coil failures are an industry problem for ALL manufacturers.

    Another reason to pull and weigh the charge!


    normal is not a troubleshooting term.

  • HVACNUT
    HVACNUT Member Posts: 6,509

    You need to see what's happening in the outdoor unit when it shuts down. Is there 24 volts to Y? Is there 24 volts coming from, or going to E/W2 on the defrost board.

    I'm assuming the defrost board that was replaced also came with the coil and ambient temperature sensors.

    Lennox definitely had a bad run of evaporator coils

    Is there an A2L system in your future?

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