Frozen Heat Pump Advice

[Mark P]

Inspected a empty home for a guy I know about 2 blocks from me this morning - outside temp around 15. The house is all electric with a heat pump. I understand that at these temps the backup electric heat on the heat pump is doing the work. My concern is that the outside unit is a frozen block of ice from where the gutter leaked and the fan cannot move. Under normal heatpump operation the fan has to operate, but I'm not sure when its in backup mode or defrost mode. It was making sounds, but I don't know if it was the fan motor or something else. I turned the breaker off to the pump thinking it may save the fan motor from burning out, but with no heat in the house, pipes might freeze, (I could not budge the main water shut off valve). Do you think I should turn the breaker back on, since that is the way I found it, even though the fan motor might burn-up, or leave it off and have the guy get a contractor out to look at it asap. ?????

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[Mark P]

Well, reading my own question a burned out fan is better then frozen pipes, and less liable to me, so I'm going back over to turn the breaker back on. I guess my real question is do you know if the fan has to operate at these freezing temps and what damage may occur to the heat pump leaving it own with the fan frozen?

[Terence McCann]

You could pull the fuse block for the condensing unit and still run the inside AHU with the electric strip heat, set the t-stat to emergency backup heat position. I wouldn't do that myself though, I'd note the condition and tell the owner to get a HVAC company out to service the unit. Last one that touches the unit buys it and with these temps it doesn't take long to freeze a house without heat.

The outdoor fan will run in the heat pump mode but it shouldn't run in the defrost mode (to the best of my knowledge). There is also a thermostat to lock out the heat pump operation below X degrees outside. Running a heat pump at 5 degrees OAT won't produce much if any heat.

[roadguy]

Kinda depends on the model/type of heat pump. Some manufacturers use one motor to turn both fans (there is a window unit in my office that is that way). If that is the case, even though the resistance heating is working, there won't be any air moving across the coils. Bad situation, either way. Needs immediate attention.

[inspector57]

Switch the indoor thermostat to "emergency" or "Aux" mode. That will kill the outside unit but keep the backup heat on. This is what that switch is for. If you pull the disconnect at the outdoor unit on some brands, you kill the low voltage that runs the whole setup. This is something I always test for on heat pumps, check for heat, backup, and kill the outdoor unit with the emergency heat setting. When we have precipitation here at below freezing, it is quite often freezing rain and can kill the balance on fan blades, quite a ruckus.

Jim

[cguffin]

All good advice.

I would call the home owner and recommend that they do what was advised here, If they can not I would get there blessing before I turned any knobs or pushed any buttons. CYA.

Thanks,

Craig

[Terence McCann]

Originally posted by inspector57

If you pull the disconnect at the outdoor unit on some brands, you kill the low voltage that runs the whole setup. This is something I always test for on heat pumps, check for heat, backup, and kill the outdoor unit with the emergency heat setting.

That's a wise idea to always check to be sure, you never know how they wire these things sometimes.

When using two transformers they are RH and RC on the thermostat sub-base. The RH is the inside unit and the RC is the outside condensing unit. If you kill power to the outside condensing it shouldn't kill the inside unit but as you mentioned better to check & know for sure.

I believe that most newer systems use the single 24v hot to power both units now.

[Mark P]

Thanks, that is all very informative, I ended up turning the breaker back on, and just telling the guy the problem and that damage may have already occured and a HVAC contractor needed to get on it asap.