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  1. #1
    Join Date
    Mar 2005
    Posts
    6

    Question

    I installed a 4 Ton Weather King heat pump and matching AHU. It was installed in July, so we set up the charge in the cooling mode. It worked great. I get a call in Febuary that the thing is not working right. I check it out and the compressor is dead. So I replace the compressor and set up the charge in heating mode. I checked the cooling mode and it was low. In short when the charge is right in heating it is to low for cooling and when it is right in cooling it is too high in heating. Any one have any ideas?

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,378
    10 SEER? 12 SEER?

    The 10 SEER uses a TXV outdoors plus a charge compensator. It is tricky to charge to make both seasons happy but with a matching indoor coil we haven't found any we couldn't get right. The 12 SEER seems especially picky. We tried to put a couple of them on coils meant for older model WeatherKing 12 SEER heat pumps with no luck.


  3. #3
    Join Date
    Oct 2004
    Posts
    3,400
    Static regain?

  4. #4
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,086
    In short when the charge is right in heating it is to low for cooling and when it is right in cooling it is too high in heating. Any one have any ideas?
    I may have a few ideas.

    First of all, how are you determining the charge on this system? Weighing in? 126 degrees over ambient on the compressor discharge while in heat mode? Superheat and subcooling? Beer can cold?

    Look at the OEM's specs for factory charge on the nameplate. Measure length of lineset and equivalent length of all fittings. Determine if charge needs fine tuning from OEM's factory charge amount.

    Ensure air handler has adequate airflow in both heating and cooling. Clean filters, clean coil, all supply registers and dampers open fully, etc.

    Check lineset to ensure it is properly sized for the system's tonnage and length of run.

    Without using superheat and subcooling readings when charging in cooling mode, you're only guessing as to what the charge might be. Pressures tell only part of the story. Going by pressures alone typically leads to an overcharge. That may have been what wiped the compressor.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  5. #5
    Join Date
    Apr 2004
    Posts
    7,680
    So give details...

    Model# for OD unit, ID Ahu and coil, psiton or TXV? Line set length, size and vertical seperation, airlfow(actual), any other details. We can tell but there are several things you should look for.

  6. #6
    Join Date
    Mar 2005
    Posts
    6

    Exclamation Details

    Here are some of the details. I do not have model numbers with me at the moment, but I will give you as many details as I can and post the numbers later. It is a 10 Seer 4 ton HP, 4 Ton AHU (04882), #82 piston indoor, Line set is about 15' 1"1/8 X 3/8. AHU is about 5' higher than HP unit. This HP unit has a scroll compressor and outdoor expansion valve. Originally charged the unit by superheat in cooling, but did have some problems getting it in range. When charged in heating mode recently went exactly by the directions and chart inside the unit panel.

  7. #7
    Join Date
    Mar 2005
    Posts
    6

    Air Flow

    I should have mentioned the air flow situation. This AHU is a downflow with the duct in the crawl. We have 10 8" flex duct supplies coming off. The longest of these is 35' and the shortest is 5'. The unit supplies a small church auditorium. The return comes through a wall and is wide open.

  8. #8
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453

    Jah

    sounds like your system does not have an accumulator. To charge this system, you would have to 'short' the cooling cycle a little to compensate for the heat cycle. But neither cycle will be its most efficient.
    I have a Lennox unit, same deal, only they loke me to service it twice a year so I just adjust the charge each time, for each cycle.
    There's not going to be a perfect way of doing it.

  9. #9
    Join Date
    Apr 2004
    Posts
    7,680
    There is indeed a proper charge but everything else has to be right, this is a heat pump and for that reason the match and installation must be correct.

    Looking at the data, it calls for a TXV indoors when matched with a 4 ton WK hp even in 10 SEER. Also, how is the return run, is there a large return plenum? If it comes in with a tight turn you can be missing part of the coil. You should have 8 slabs in that coil (4 a's). If its tight consider turning vanes.

    You also need to know your actual air flow, not calculated by duct design. Might I suggest using the heat rise method.

    Also can you recall if the flaps were folded out on the air handler at the plenum? If they werent, thats about a 25% airflow reduction. You may have to pull the blower to see, but you can do that when you install the TXV.

    Your lines sound ok.

  10. #10
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,378
    Imagine that, it does! We've never installed a PJ heat pump that big so didn't realize they called for a TXV. Those cube pumps have been such a pain in the #$# to us with their crazy coil matchups and problems in the outdoor unit.

  11. #11
    Join Date
    Mar 2005
    Posts
    6

    Heat Pump

    There is no sharp turns in the return plenum. It actually goes into the drop ceiling space and a 30 X 30 grill on the wall.
    I don't see that as a problem, but I did wonder about the TXV. When I asked my distributor about it they told me that I did not need it, but like you I think it is probably where the problem is.
    My next move was to put a TXV on the indoor coil and change the 3/8 line to 1/2. If you say the 3/8 is ok I will just start with the TXV.
    I know the flaps are folded out. In fact, the distributor told me that I could not just set it on a box that extended into a plenum into the crawl, but I needed a 10" straight flange off the AHU flange in order to generate the proper air flow. I didn't see how that mattered, but I did it as they said.
    I will check the heat rise, though. That would be a good information check.

  12. #12
    Join Date
    Apr 2004
    Posts
    7,680
    Dont put a 1/2 in line in, that goes against the instructions also.

    When you add the TXV, do this....

    Recover the refrigerant, dont pump it down. Add the TXV and then add the drier. Tripple evacuate. break with nitrogen the fiorst two times and then refrigerant on the third. Weigh in the charge per the label.

  13. #13
    Join Date
    Apr 2004
    Posts
    7,680
    Originally posted by BaldLoonie
    Imagine that, it does! We've never installed a PJ heat pump that big so didn't realize they called for a TXV. Those cube pumps have been such a pain in the #$# to us with their crazy coil matchups and problems in the outdoor unit.
    The 12 SEER requires the TCQC coil too, no option for the multiflex.

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