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AC running during heat mode


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Todays inspection was a new home with gas fueled condensing furnace.

I had not yet begun to inspect HVAC but while I was on exterior portion I noticed the Lennox 13ACX air conditioner running. Outside temps were 40 degrees so I thought it not good for the unit to be running. I went inside assuming that the buyer or agent had been fiddling with the thermostat. I was planning on telling them to turn off the AC since it was cold outside. But to my surprise, the thermostat was actually in the heat mode.

I know about hybrid systems but isnt this Lennox 13ACX and air conditioning unit only? What would cause it to be running during the heat mode? Both of the refrigerant lines were insulated when normally I only see the low side insulated. While this thing was running, the low line (fat one) was warm and the high line (skinny one) was cold. I turned the thermostat to the off position and let it wait a while. When I turned it back to heat the gas furnace fired up and I could not duplicate the AC running during heat mode.

Is the Lennox 13ACX AC only or heat pump? The Lennox site indicates AC.

I don't understand what's happening here. Help me understand please.

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Maybe this is it. The AC could be part of a Humiditrol system.

The features button at this site says the 13ACX is compatible with such a system. Perhaps the unit was responding to a humidity adjustment and had nothing to do with the heat setting.

http://www.lennox.com/products/air-conditioners/13ACX/

If not, any help in understanding would be appreciated.

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A brief search yielded nothing that would suggest that the ACX was available as a heat pump.

The vapor line (fat one) would be hot , not warm, in heat mode. In 40 degree ambients in AC mode, it would be warm.

Sounds like a defect. Refer to AC contractor.

Marc

EDIT: The Humiditrol system might be it. Never seen such a system before.

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If it's equipped with a Humiditrol, you would clearly see the dehumidification coil downstream of the AC/HP coil. There would also be a Tee in the AC/HP vapor line.

If it's a HP, the model number would have XP or HPX. Did you see a reversing valve in the outdoor unit?

A reversing valve was the first thing I looked for and I did not see one.

At the Lennox website, they list the 13ACX as compatible with Humiditrol. Go to the link below, click on the features button and scroll down. It says "Designed to work with the Humiditrol? whole-home dehumidification system"

http://www.lennox.com/products/air-conditioners/13ACX/

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I'm not familiar with that systems components, but in general a separate coil would not be needed.

Simply running the a/c will remove humidity winter or summer.

This could simply be a control issue to allow the humidistat to run the a/c during the heating mode.

If you want to shift the split between latent-heat (moisture) and sensible-heat (temperature) removal towards greater latent-heat removal, then a different coil with different specs is one way to do it. That might be the reason why this Lennox accessory has an additional coil mounted just after the evaporator coil.

I'm sure there's other ways to do it. I don't know how this particular system does it.

My wholesaler doesn't sell Lennox so I don't have access to that info.

Marc

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If it's equipped with a Humiditrol, you would clearly see the dehumidification coil downstream of the AC/HP coil. There would also be a Tee in the AC/HP vapor line.

I'm going to check again when I go back for radon pickup.

It's weird you know. Sometimes one misses obvious things that we generally are not looking for. For instance, I don't pay much attention to most low voltage wiring. But you would be surprised how many clients ask me about it. They see it but my mind just automatically bypasses it since I'm not looking for it.

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I know what you mean. Sometimes, if time permits, when an inspection is finished, I walk around once more, deliberately trying to look at nothing in particular, just look, and I see things well deserving of mention that I hadn't yet noticed.

Marc

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