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Thread: Help Heatpump freezing

  1. #1
    DIY Junior Member tilhasbb's Avatar
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    Default Help Heatpump freezing

    Hello,

    I have a Lennox HP19 system that is around 15 years old. The compressor died 5 years ago and it was replaced.
    Last year this same issue started happening at the end of winter and we never fixed it. In summer it cools perfectly and uses minimal electricity. I've washed, cleaned everything and replaced the filters. First day of winter it worked perfectly (first time I switch it from cooling to heating). Today it froze again...
    I have two questions.
    1) Is it worth repairing or buying a new system? since it is old.
    2) What could the problem be?

    Thank you in-advance
    You can find the full resolution photos here Name:  Photo 2013-10-24 10 17 48 AM.jpg
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  2. #2
    Nuclear Engineer nukeman's Avatar
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    My guess is that you have a stuck reversing valve or something like that. This would case it to stay in AC mode. This would overcool the indoor coil and case it to freeze. Along the same lines, it could be a problem with the defrost control board. The outdoor coil can freeze up during heating mode. To avoid this, the unit puts itself into defrost mode (flips the reversing valve to AC mode and pulls heat from inside the house to heat the outdoor coil). During defrost, the aux. electrical heating strips will kick on so that the air blowing in the house wouldn't be cold.

    I would have a tech come look at it. You can also post the problem over on hvac-talk.com. They have a lot of hvac pros on there. They are anti-DIY over there, but could probably tell you what they think it might be (but they probably won't help you fix it unless it was something simple (like a dirty filter)).

    One thing that you can do is feel the refrig lines at the outdoor unit with the unit running (after things have thawed out). One should be quite warm and the other will be closer to room temperature (still warm compared to outside). If the lines are cold (especially if colder than outside temp), this would indicate that you are stuck in AC mode.

  3. #3
    DIY Junior Member tilhasbb's Avatar
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    Thank you. What bothers me is that it ran for the first 2 days I switched the system to heating. I was getting 50C (122F) till the house warmed up.
    I checked the lines and one line was very hot and other was cool. Now one is frozen and other is very cold


    So I waited about 5hrs for everything to melt. I turned off power from the main circuit break to everything.

    I turned it back on now and i only put the thermostat a few degrees more than the ambient temperature to be sure its only heat not emergency heat. It works perfectly now... I got an infrared thermometer. Ambient is 16C (61F) , thinner hose is 24C (75F) and wider hose is 60C (140F).
    I also checked the 3 way valve outside and 2 were cool (outside coil and compressor side) and the one going into the house very hot.
    Last edited by tilhasbb; 10-24-2013 at 10:09 AM.

  4. #4
    Nuclear Engineer nukeman's Avatar
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    If the reversing valve is sticking, maybe it only sticks some times? That could explain it. The valve cycles during each defrost cycle, so it could get stuck in heat mode or AC mode. Sounds like maybe the issue (or a faulty defrost board doing the same thing).

    Anyway, it sounds like someone will have to check the system over to see what is going on. If you find the problm, please report back. It will be interesting to see what the problem was.

  5. #5
    DIY Junior Member tilhasbb's Avatar
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    Quote Originally Posted by nukeman View Post
    If the reversing valve is sticking, maybe it only sticks some times? That could explain it. The valve cycles during each defrost cycle, so it could get stuck in heat mode or AC mode. Sounds like maybe the issue (or a faulty defrost board doing the same thing).

    Anyway, it sounds like someone will have to check the system over to see what is going on. If you find the problm, please report back. It will be interesting to see what the problem was.

    I'm searching to see how I can test the board. I hope it is that because I found the "Lennox Defrost Kit Control Board Thermostat " kit for under 200$ and it seems easy to replace. If not I searched and there are only two Lennox authorized repair guys in my area and both want 150$ for diagnostic and are not available this week.... I'd rather test the board. If it is that I'll order and replace it myself. If not then I'll call for an estimate to replace the reversing valve and I'll see if it's worth patching it or replacing the entire system.

    BUT I'm thinking now, is it possible to DISABLE the defrost cycle? so the reverse valve does not switch to AC mode and get stuck?

  6. #6
    Nuclear Engineer nukeman's Avatar
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    First thing is to look at the wiring diagram in the unit (or find additional info). Some units put 24v (usually) to the reversing valve for heat mode and others apply voltage for cool mode. Once you know, you can test the reversing valve to see if the correct voltage is there for heat mode (normally either 0v or 24v AC). If the voltage seems okay, then the defrost board is probably okay and the valve itself is just sticking. If this is the case, if it starts to freeze up again, you can knock the valve with a wooden block or similar (after seeing that it is getting the right voltage) and see if it switches modes. If it is the case, you probably need a new reversing valve. With the cost of pumping down the system, replacing the part, refilling the system, etc., it may not be worth it since it is an older unit.

    In terms of disconnecting the defrost board, you could try for testing purposes (depending on what the reversing valve needs). However, you can't leave it disconnected as the outdoor unit will turn into a block of ice with the heat pump operating normally.

  7. #7
    DIY Junior Member tilhasbb's Avatar
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    Thank you!
    Here is the HP19 Manual on page 5-6 they talk about the defrost board http://www.completeheating.ca/manuals/LennoxHP19.pdf
    I found the 24Volt pin. So what I should do is check it with a volt meter now and see if it's 0-24V then, check it again when it is in defrost mode if it is 0-24. It should be opposite.
    Now how do I know when it is in defrost mode?


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  8. #8
    Nuclear Engineer nukeman's Avatar
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    Looks like a nice manual. It says that the reversing valve is energized for cooling or defrost. You might put it in AC mode and check the voltage at the reversing valve (set your meter to AC, should be ~24v). Once you do that, turn off the AC and wait a few minute (many systems have a 5 minute lock out to prevent the compressor from starting when you switch modes or after a power outage). Once it is in heat mode, verify that no voltage is present at the reversing valve. If the heat has just started, it should not be in defrost mode. During normal operation (for heat), when it defrosts, the outdoor fan should turn off and you will hear the compressor continue to run. The you will hear a "whoosh" and it starts back up. The noise is from the reversing valve while it throws the flow of refrig. in reverse.

    If you continue to get voltage to the reversing valve when the heat first starts, this could be a defrost board problem. If this is the case, we can try some of the tests in the manual and see what we find.

    If the board is faulty, it could be putting it into defrost when it shouldn't be in defrost. The other possibility is the board is working, but the valve is physically sticking. I did read on hvac-talk that the reversing valve should be replaced after a compressor burn-out. Depending how the compressor failed before, it could have damaged the reversing valve or other parts.

    Anyway, let's see what voltages you are getting at the reversing valve and we'll go from there.

  9. #9
    DIY Junior Member tilhasbb's Avatar
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    This is weird.
    System on AC, I got 27.6Volts. turn off system and wait 15minutes, check voltage is still 27.6V
    Turn Heat on, I get 27.1Volts.
    But I check the temperature of the coils and it's working perfectly. 3C (37F) Coils, 10C (50F) from Compressor, 60C (140F) to house.
    Hot air is coming from the air vents 33C (91F)
    I waited 15 Minutes, while the system is on heat and the Voltage still reads 27.1Volts

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  10. #10
    Nuclear Engineer nukeman's Avatar
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    Try to measure directly at the reversing valve. It could be that you tapped into the wrong wire and you are measuring the 24v voltage that is powering the defrost board.

  11. #11
    DIY Junior Member tilhasbb's Avatar
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    Ill look for the reversing valve.
    As I'm doing that here is two videos
    http://youtu.be/9gDwKJL5NnM (Turning AC on and Off)
    http://youtu.be/CzyxIcZMbVs (Turning on Heat from Off)

  12. #12
    Nuclear Engineer nukeman's Avatar
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    Should be it in one of your earlier pics (to horizontal pipe to the left of the compressor w/ several large pipes coming off vertically). There should be an electrical connection there w/ two wires. Those wires should trace back to the defrost board (looks like there is a defrost relay between the defrost board and the reversing valve).

  13. #13
    Jack of all trades DonL's Avatar
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    It would not hurt to clean that PCB. And look for a blown capacitor. C2 could be a suspect. Or maybe you got coil cleaner on the board ?

    It looks like IC pins 1-10 has signs that a Cap may have blown and acid has collected there.

    That board should be protected but Mexico must not have believed in conformal coating.
    I would add it.

    It also looks like the high pressure service valve has growth on it, and may be missing the valve cap, and it Will Leak !.


    Good Luck.
    Last edited by DonL; 10-26-2013 at 06:46 AM.
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  14. #14
    DIY Junior Member tilhasbb's Avatar
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    I will check on Sunday as it's raining cats and dogs outside all day.

    I kept checking the multimeter and it did go to 0V.

  15. #15
    Nuclear Engineer nukeman's Avatar
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    Just seeing if you ever figured this out...

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