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problem with carrier heat pump

does anyone know if the txv used on a carrier air handler model# fk4dnb006 has a internal check valve? i worked on one today matched with a 38ykc048 heat pump that works fine in the cooling mode,but when it is in the heating mode it immediately (within 30 seconds) freezes at the piston body,and the distributor on the outdoor unit.all four tubes that come off the outdoor distibutor freeze to the same degree.the only thing that i can think of would be a stuck (closed) check valve at  air handler. that would explain why it operates fine in the cooling mode.the unit will go into defrost,but by that time there is so much ice on the outdoor coil it times out before all the ice can clear the coil. any thoughts or suggestions would be much appreciated. thank you


  • don_9
    don_9 Member Posts: 395

    Take a look at the piping.if the txv does not have a internal check valve you would see a bypass with check valve going around the txv.If you do not see the bypass then it has a internal check valve.

    It possible you could have a stuck check valve on the indoor unit and if so you would see high head pressure if someone added freon before you.If not then it would be below normal with a suction pressure being low.

    I would start at the outdoor metering device.Check your superheat at the outdoor coil that would lets you know if she is starve for refrigerant.Then you have the filter drier that you could check temp drop across it to see if she clogged, all tho pressure taps would be far better for checking a clogged drier.

    Its been my experience when they freeze that quickly it low on refrigerant or the outdoor txv is bad.
  • John Mills_5
    John Mills_5 Member Posts: 935

    frosts at the point of the restriction. Might want to investigate the outdoor piston. I'd think if the issue were indoors, you'd see frost on the outlet of the TXV. 
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