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  1. #1
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212

    Guide to Heat Pump Operation for a specific model.

    This is my first post to commercial. I have pretty much confined all
    prior posts to the safe residential zone.

    However, today I was presented with troubleshooting a 10 (12?) ton
    commercial heat pump and the schematic only got me so far.
    There must be about 15 wires into the defrost board, a sharp contrast
    to one for residential.

    I googled the operaton info for the Carrier (50HJQ012-631) but it did not
    give me any info about the inputs/outputs of the defrost board.

    As memory best serves me, the #1 compressor worked fine, giving
    about a 15+ temp rise at the unit. But the #2 compressor would
    run for about a minute and stop. For those who are intimately
    familiar with such units, the relay (CLO2) seemed to have only one input
    pin 2, and one output, pin 3. But pin2 came, I think, from the defrost
    board. And it had maybe 15 wires to it and the operation info presented
    absolutely no info about operaton of the board.

    It seemed strange to me that there did not seem to be merely a duplication
    of circuits of #1 for #2. They seemed different.

    The two safeties, LPS and HPS , lie after the CLO2 board, and just before
    the contactor for the compressor. The defrost sensor, I forget, but I think
    goes to the defrost board. On the running compressor, comp1, pins 2 and 3 of
    CLO1 have control voltage. On the stopped compressor, pins 2 and 3 of
    CLO2 have no control voltage. As I said, the LPS and HPS lie after
    CLO2 so I leaned toward them not influencing signals TO CLO2,
    but maybe I'm wrong?

    Basically, if I knew what ALL of the terminals on the defrost board meant,
    I would be in a LOT better shape to troubleshoot this thing.

    Can anybody enlighten me? I go back tomorrow at 7:00am.
    I am SO glad I will be merely facing low 30 temps, that I don't
    live back east (or midwest where I grew up). I don't know how
    HVAC men back there make it through the cold season without
    death finding them. You all don't get paid enough to be on a
    rooftop in freezing temps. Then again, maybe you all have
    more sense than to install heat pumps rather than gas-packs.

    Thank you for any help.

  2. #2
    Join Date
    Jan 2013
    Location
    San Gabriel Valley, California
    Posts
    32
    take some clear picture on the wiring schematics inside the unit, and post them here... then i will be able to tell you what to check...

  3. #3
    Join Date
    Jan 2013
    Location
    San Gabriel Valley, California
    Posts
    32
    My freind I did spent sometimes and tried to look for the orginal wiring diagram, couldn't find it... but let me kinda tell you what to check right now..you are going too far, you don't need to know how the defrost board works for now.....

    1. with the unit off, put your gauge on the compressor which was not working right, put a amp clamp on a high voltage wire that goes to the compressor from the contactor..

    2. turn unit on, watch carefully at your amp meter and write down the highest amp draw at the beginging when the compressor kick on(LRA), compare to the name plate, see if it exceed the limit.. if it exceed the limit, you need a new compressor...but watch the pressure on your gauge to make sure too.. because if the compressor is seized up, your pressure will no move..... but if your pressure change, wirte down the pressure, and the compressure loading amps and compare it..

    3. if the compressure shut off after it turn on, what was the pressure before it shut off? if it's too high, your high pressure switch might be open,then check your air filter clean them.. if it's too low, unit low on charge and might has a leak... anyways, any of the safety open it will trip on CLO...

    4. so , after compressor is turned off, check your CLO that goes to your problem compressor to make sure.
    put your meter on 2 and common/ground you should get 24v( if you don't get 24v here, u might wanna check economizer), then check 3 and common/ground, if you get no voltage, your CLO is Locked out. Carefully pull the #1 wire out on the CLO will reset it..

    let me know.....make sure u check voltage balance too, on the wires that go to the compressor...

  4. #4
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    there's no email in that profile!

    this is an open forum
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  5. #5
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,595
    Rather than google'ing tr exact model, look for the iom of that series of machine or go directly to the carrier website. I haven't seen one of these machines before, but from the sounds of it you're making things more complicated than it needs to be. Attack it in the same way you would a residential unit. That's what that one circuit is, just bigger. Remember it's the KISS method.

  6. #6
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212
    What is "voltage balance?"
    Sorry about my ignorance.

  7. #7
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212

  8. #8
    Join Date
    Feb 2006
    Location
    Phoenix,AZ
    Posts
    2,891
    Carrier RTU's have all that crazy wiring just so you can use a conv. heat cool tstat and not a heat pump stat with a o terminal. lol

  9. #9
    Join Date
    May 2012
    Location
    Upper Michigan
    Posts
    3,588
    Fenghvac this is an open forum, every Tom dick and Harry can see you trouble shooting info. Now when a homeowner has a heat pump they can't get running there going to come here read everything you said and lose a testicle one way or another. We have closed forums and once you apply for pro membership you can access them and say whatever you want. This isn't a DIY site, there are many highly skilled techs behind closed doors.

  10. #10
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212
    Early morning, before going back to work.
    A little light bulb came on when I woke up.
    CLO. Compressor lock-out? Duh.

    It has been a couple years since I came across
    those circuits, so C-L-O didn't dawn on me yesterday.

    So, yes. Things are probably much simpler than
    I was making them. Likely it was the low-pressure
    switch. I'll put my gauges on it today.

    But I still would like to know what all of those terminals
    on the defrost board do--because I just KNOW that not
    knowing is going to make some day in my future very,
    very stressful.

    (Sorry, I don't have clear picture-taking ability.)

    Thank you.

  11. #11
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212
    This morning I disabled compressor #1 and started compressor #2
    in cooling. I had my gauges on and my amp clamp on the compressor
    wires. I'm not sure what voltage balancing is, but the three only deviated
    by .1 to .4 amps. Is that okay?

    Pressures/temps were rather low. It almost pulled to a vacuum.
    I advised the guy in charge, charged the circuit, verified performance.
    I think it is all okay until he decides how he wants to pursue the leak.

    I have a bunch of Carrier links to pursue in hopes of finding out
    a bit more about the defrost boards. This account has maybe six
    other Carrier heat pumps so odds are I will likely need to know
    eventually.

    Thanks again for everyone's help.

    (Yes, the way they call for heat really threw me on my first maintenance
    visit to this customer. I was trying to jumper as I would your typical
    residential heat pump package and things were not working. It was
    stressful until I made the discovery. I think I checked control voltages
    on a unit running from the thermostat.)

  12. #12
    Join Date
    Jan 2013
    Posts
    20
    On commercial units Carrier can give you details on the exact defrost boards installed in the units. You would need the Serial Number and Model Number just as you would to source the board.

  13. #13
    Join Date
    Feb 2006
    Location
    Phoenix,AZ
    Posts
    2,891
    The board is like any other waiting for the DFT to close and at a selected time it sends power from the hot side (R) of transformer to the reversing valve and also W2 heat strips if equipped. The diagram you posted shows the N.O. contacts on the board.

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