I have a newer Duotherm 15000 BTU heat pump that now ices up on the condenser coil, which I guess could be called the evaporator in heat mode. It produces a real iceberg until I notice it by looking up on the roof and the whole backside is solid ice. My old Duotherm had a control mechanism that would shut the fan off then reverse the freon flow so the outside coil would heat up and melt the ice. I'm sure this is supposed to do that too. It has the same control box and CCC thermostat. Is there some outside sensor that is malfunctioning?

Coil iceing can generally be traced to low air flow across the coils. Either that or the unit has a leak and its low on gas.

I can not speak about the Duo Therm, however I heat my home with heat pump system. When using the AC as a heat pump the coils do freeze up, however my system does defrost the coils also. It sounds like you need your system checked.

Does it go through the periodic reverse flow & fan off defrost cycle? I'm sure there is an external temperature sensor that contributes to the control of that, but mine have never malfunctioned so I can't be much help.

Definitely my old DuoTherm went through the periodic defrost cycle when it was cold enough outside. But this one seems to not do it. But I believe it has to to work properly in the 30 degree range. That's why I wondered if someone knew of a sensor that told it it was icing up. It's not low on freon. I'm familiar with that aspect of freezing up. This has never frozen up in cool, which the evaporator would do if low on freon. Its only a year and a half old.

Mine goes into a defrost mode which shuts off the interior fan and reverses the valve to heat the outside coil by running the compressor only. Pretty sure it’s controlled by the ambient temperature sensor because it doesn’t do it at all temps. Makes a heck of a noise when the valve reverses.

DuoTherm Heat Pump Icing Up | Good Sam Community

16 Replies

howardwheeler
Explorer
Dec 13, 2018
yes, that is exactly what mine used to do, and the first time I heard it I thought it was going to explode. But it no longer does that. Instead the outside coil becomes like a glacier and it takes a while for it to thaw. I need to know what sensor controls that.
I-Can-Am-Can-Yo
Explorer
Dec 13, 2018
Mine goes into a defrost mode which shuts off the interior fan and reverses the valve to heat the outside coil by running the compressor only. Pretty sure it’s controlled by the ambient temperature sensor because it doesn’t do it at all temps. Makes a heck of a noise when the valve reverses.
howardwheeler
Explorer
Dec 13, 2018
Definitely my old DuoTherm went through the periodic defrost cycle when it was cold enough outside. But this one seems to not do it. But I believe it has to to work properly in the 30 degree range. That's why I wondered if someone knew of a sensor that told it it was icing up. It's not low on freon. I'm familiar with that aspect of freezing up. This has never frozen up in cool, which the evaporator would do if low on freon. Its only a year and a half old.
Ductape
Explorer
Dec 13, 2018
Does it go through the periodic reverse flow & fan off defrost cycle? I'm sure there is an external temperature sensor that contributes to the control of that, but mine have never malfunctioned so I can't be much help.
craig7h
Nomad II
Dec 13, 2018
I can not speak about the Duo Therm, however I heat my home with heat pump system. When using the AC as a heat pump the coils do freeze up, however my system does defrost the coils also. It sounds like you need your system checked.
donn0128
Explorer II
Dec 12, 2018
Coil iceing can generally be traced to low air flow across the coils. Either that or the unit has a leak and its low on gas.

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DuoTherm Heat Pump Icing Up

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