Heat Pump Question(s)

[fqp25]

Is this normal? 32 degree outside temp. New construction vacant for 2 years, t-stat set to 63 degrees.

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Couldn't this be damaging?

When I got inside I turned the t-stat up to 65, and the Aux light turned on and the heat pump turned off. Shouldn't the system switch to axillary heat when the outside temp drops below 40 degrees or so?

Frank

[Jim Katen]

Is this normal? 32 degree outside temp. New construction vacant for 2 years, t-stat set to 63 degrees.

Couldn't this be damaging?

When I got inside I turned the t-stat up to 65, and the Aux light turned on and the heat pump turned off. Shouldn't the system switch to axillary heat when the outside temp drops below 40 degrees or so?

Frank

Unlikely to be damaging. No it's not normal. The system should go into defrost mode often enough to prevent that. You might have a problem with the defrost control or the system might be undercharged.

If that system uses electric heat strips as auxiliary heat, no, the outdoor unit will continue to run but the heat strips will supplement it.

- Jim Katen, Oregon

[Terence McCann]

Couldn't this be damaging?

When I got inside I turned the t-stat up to 65, and the Aux light turned on and the heat pump turned off. Shouldn't the system switch to axillary heat when the outside temp drops below 40 degrees or so?

Frank

When the t/stat is jumped numerous degrees above room temp the aux heat comes on (electric strip heat in an all electric application) and the heat pump operation stops. The heat pump operation will operate normally when a normal drop in room temperature is noted. Without looking at the operation manual though I have no way of knowing what the sequence of operation is. For a cut-off outdoor ambient temperature, that will lock out the heat pump, the operation manual should be consulted. If I were to guess I would say 15 to 20 degrees??? maybe lower with newer units?? In any case it would not be damaging to the unit. When the unit switches to full electric strip heat, and shuts off the heat pump, it is acting just like a normal electric AHU.

Suggest you plug in the Make and Model of the unit and doing a Google search for the manual.

EDIT:

I must be losing my eyesight... I looked at the pics again, after Marcs post and saw that the heat pump was a block of ice.

What Jim and Marc said....

[:-dunce]

[Marc]

You bet it can be damaging. It's takes heat to evaporate liquid refrigerant to a gas and if the coils are clogged, with ice or whatever, it may remain as liquid, all the way to the compressor suction. Pumps move liquids, compressors move gases. Inject liquid into a compressor like a residential refrigerant hermetic unit and you'll blow the valves for sure.

Marc

[Jim Katen]

. . . Inject liquid into a compressor like a residential refrigerant hermetic unit and you'll blow the valves for sure.

Unless it's a scroll compressor . . .

- Jim Katen, Oregon

[Marc]

The scroll is more tolerant to contaminants than reciprocating units with reed valves, but they can be damaged too and can fail if too much liquid refrigerant and oil enters the suction, don't you think Jim?

Marc

[Chad Fabry]

pumps move liquids, compressors move gases.

What does a vacuum pump move?

[Marc]

Gases.

[Jim Katen]

The scroll is more tolerant to contaminants than reciprocating units with reed valves, but they can be damaged too and can fail if too much liquid refrigerant and oil enters the suction, don't you think Jim?

Marc

I think it probably can be damaged, I've just never seen or heard of it in my area. Liquid seems to squirt through scroll compressors without causing harm, at least for a while. Most of the heat pumps here have high head pressure safety cut offs that have to be manually reset. Don't they have those in HPs in the south?

- Jim Katen, Oregon

[Marc]

Up until about 5 years ago when I last worked full time in HVAC, yes. Practically all of them. When they are tripped, it's usually been because someone flipped the thermostat from heat to cool or vice versa too quickly, spiking the head pressure long enough to trigger it. Don't see reciprocating compressors in residential/ light commercial HVAC units anymore, except for perhaps Trane. Commercial coolers/freezers still use them (last I heard).

Marc

[Jim Katen]

Up until about 5 years ago when I last worked full time in HVAC, yes. Practically all of them. When they are tripped, it's usually been because someone flipped the thermostat from heat to cool or vice versa too quickly, spiking the head pressure long enough to trigger it.

It used to be a real problem with the old mercury bulb stats because the mercury would bounce back & forth causing the compressor to start/stop/start. I don't see that much with the newer electronic stats.

Don't see reciprocating compressors in residential/ light commercial HVAC units anymore, except for perhaps Trane. Commercial coolers/freezers still use them (last I heard).

Trane held out for a long time, but all of the new Tranes that I see have scrolls. Now they bray about it as if they invented them.

- Jim Katen, Oregon

[inspector57]

Is this normal? 32 degree outside temp. New construction vacant for 2 years, t-stat set to 63 degrees.

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Click to Enlarge

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When I got inside I turned the t-stat up to 65, and the Aux light turned on and the heat pump turned off.

Frank

Just a fine point, in the normal heat mode, the normal operation sequence would leave both the heat pump and strip heaters engaged unless there is a outdoor stat to shut the HP down or the indoor thermostat mode switch is moved to the "emergency" heat setting.

IMO you may have a unit that is not wired correctly or has a malfunction in the control circuit.

Around here, we may only have a 5K heater as supplemental heat and the unit may never catchup if the HP is shut down when the temperature falls below the set point.

No doubt that frost load on the coil is a tad bit on the heavy side so the defrost cycle needs attention.