Will thermostat show heat pump in defrost mode

richard904March 14, 2013

We have a Trane XL16i with a Honeywell VisionPRO IAQ thermostat. When the heat pump is on, the thermostat shows Heat On mode, but even when the heat pump is defrosting the Aux Heat On does not show. When there is a several degree temperature variation between requested heat and actual heat it does show the Aux Heat On. Is this the expected information in the defrost mode?

Our old system with its very simple thermostat would show the aux heat on light when the system was in defrost mode.

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Here is the installation manual. I am not sure if it is exactly the model you have. There is no mention of auxiliary heat being displayed during the defrost cycle.

Here is a link that might be useful: Honeywell Visionpro IAQ thermostat

    Bookmark   March 14, 2013 at 5:20PM
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I looked at the link you gave, and at all the manuals I had, and indeed there is no mention of this. I presume then the heat pump communicates directly with the air handler to turn on auxiliary heat through a "back channel" so to speak, and the thermostat is unaware of this or does not care.

    Bookmark   March 16, 2013 at 10:57AM
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Richard, you are correct. The heat pump controls auxiliary heat signal to indoor air handler. When the thermostat calls for aux heat, then it will display on the screen itself.

This post was edited by ryanhughes on Sat, Mar 16, 13 at 11:53

    Bookmark   March 16, 2013 at 11:52AM
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Mine does not show when the unit is in defrost but I plan to use some spare thermostat wires and send a signal up to some leds behind the stat that will signal defrost mode and aux mode and cast light behind the stat.

It is rarely in defrost unless we are having some sort of moisture event close to or below freezing which is why demand defrost is awesome.

    Bookmark   March 17, 2013 at 11:05PM
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I have a carrier heat pump with a carrier oil furnace for Aux Heat... a Carrier Edge Thermostat.

When HP is in defrost mode, the thermostat shows "Aux Heat" as heating mode.

    Bookmark   March 18, 2013 at 10:11AM
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