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Old 11-21-2011, 10:59 PM
3 posts, read 21,925 times
Reputation: 11


My husband installed a new thermostat. It is totally different from the one we had previously. When I turn the heat on, I notice that the outside A/C unit is kicking on..We have lived here 10 years, and I've never noticed that before. Is this a normal thing? I can't believe I've never noticed before..
We have a gas heater/heat pump, and the A/C runs on electric..My husband has left for Afghanistan, and he's not sure either if this is right. Any ideas?
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Old 11-21-2011, 11:15 PM
27,629 posts, read 63,123,705 times
Reputation: 16996
You almost certainly DO NOT have a gas heat pump. Those tend to be used only in large commercial buildings. You may a gas furnace AND a heat pump. It is likely that if you have such a "dual fuel" system you did NOT use the proper type of thermostat. With hubby overseas I would try to ask for assistance from local professionals, ideally those that are trustworthy and may have some connection to the military themselves.

BTW dual fuel systems are relatively rare, especially in a ten year old house -- http://www.heat-pump-review.net/dual...at-pumps/guide PPS Heating
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Old 11-22-2011, 02:44 PM
Location: Sarasota FL
5,966 posts, read 7,519,759 times
Reputation: 5155
If you actually do have a heat pump I would first check to see that the new thermostat is for a heat pump. I've seen people who purchased a AC/heater thermostat somehow get it wired where the A/C function works but the heat function doesn't. Some get heat but no AUX where the pump is off and only strips are used or only the strips are used and the pump doesn't come on.
If you have a gas heater and a geat pump, I'll assume there are two separate sets of wires from both attached to the thermostat. Some of the wires are probably on the wrong terminals.
btw- I understand 'lived in the house 10 years', not that the house is ten years old. Some older homes have odd systems. My brothers house has a small oil burner in the kitchen 'mud' room for hot water and base board heating with it's own thermostat and a central AC [only] system with a thermostat
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Old 11-22-2011, 08:00 PM
Location: Knoxville
4,040 posts, read 18,270,187 times
Reputation: 4543
Gas heat pumps are actually pretty common. The gas furnace acts as the EMERGENCY heat. In moderate temperatures, the unit acts as a regular heat pump, using the outside a/c unit to provide heat. When AUX or EMERGENCY heat is required, the gas furnace kicks in.

The easiest way to tell if it is a heat pump is to turn on the heat, just a couple degrees above room temperature. When the outside unit kicks on, go outside and put your hand on the large refrigerant line (or fitting) at the bottom of the unit. The large line will have the black foam insulation on it.
After the unit has been running a couple of minutes, that pipe should feel Warm to HOT. If it is, then you have a heat pump.

However, if the pipe feels Cold, then you have a mis wired thermostat and the air conditioning is coming on.

Hope this helps.
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Old 11-22-2011, 08:01 PM
3 posts, read 21,925 times
Reputation: 11
We bought the house new, so it is 10 yrs. old. I'm not sure about the system other than the gas furnace is up in the attic, and the a/c unit is outside. I finally just put the heat on last night to see if heat would come out, and it does, but the a/c unit outside is also kicking on. The thermostat we bought was for a heat pump. When the heat is on, it also says "AUX on" on the thermostat..Where is the heat pump located if I have one..(sounding really dumb blonde here )..
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Old 11-22-2011, 09:37 PM
27,629 posts, read 63,123,705 times
Reputation: 16996
The outside unit is for the heat pump and A/C.
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Old 11-22-2011, 11:34 PM
Location: Johns Creek, GA
10,649 posts, read 41,411,308 times
Reputation: 11102
Understanding how different HVAC (Heating, Ventilation, and Air Conditioning) work will help you in explaining different scenarios.
Air conditioning works like this: Figure #1
Heat pump works like this: Figure #2
Notice that the "system" is the same- the only difference is the directional flow of refrigerant.

Auxiliary heat/ emergency heat is a standard gas or electric furnace that supplies heat when the ambient outdoor temperature reaches a point where there is not enough heat molecules to raise the temperature inside the structure.
My take on the situation is this- either the old thermostat wasn't wired correctly (assuming the new is), or it was the wrong type and you never had "heat pump" heat- it was always the "aux" heat. Considering you never noticed the condenser running before.
Attached Thumbnails
new thermostat installed~new problems-air-source-cooling.gif   new thermostat installed~new problems-air-source-heating.gif  
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Old 11-23-2011, 06:01 AM
1,138 posts, read 2,294,673 times
Reputation: 848
I'd take chet's advice and find a local professional to help out. There are a lot of things it could be. For example, the thermostat may be set to the wrong type of HVAC system. Or the wiring in the thermostat may be incorrect and causing your outside AC unit to turn on.
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Old 11-23-2011, 07:42 AM
Location: Lexington, SC
4,281 posts, read 9,588,440 times
Reputation: 3677
I had a similiar situation some years back when I tried to install a programmable thermostat in place of a mechanical one on a heat pump system.

I understand this stuff more then most and I could not do it. I had to hire someone in the business to do it for me.
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Old 11-24-2011, 07:51 PM
27,862 posts, read 31,468,812 times
Reputation: 3989
What brand HVAC system do you have?

What brand thermostat did you buy? Is it digital?
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