Heat pump or not!!

Question for someone with more knowledge then me.

1993 home has a Trane heat pump at exterior.

Furnace is gas Trane brand also 1993.

Thermostat has no emergency heat mode.

My question is about the heat pump mode and configuration.

How does the exterior electrical, heat pump box near interior components function? Had power when I opened small box for heat pump.

It appears to be a gas furnace with an electric AC unit but I could not tell if the Heat pump mode operated or was functional.

How does the system know how to switch from gas, electric heat pump mode if no emergency heat function at the thermostat.

I could use some explaining, education on this one.

Thanks, see pics.

229212 005 (Small).JPG

229212 005 (Small).JPG

229212 052 (Small).JPG

229212 005 (Small).JPG

229212 056 (Small).JPG

229212 046 (Small).JPG

229212 058 (Small).JPG

They are called dual fuel the out side units operate on exterior temp and thru the add on box shifts auto to the gas furnace when the exterior temps drop to the desired setting. I have a propane furnace for my heat pump but do not have the add on box came factory wired with a external temp sensor.

Your furnace was most likely installed with a standard A/C and the owner got sold a heat pump at a later date. Did the date of MFG match or were they different.

I know they are duel fuel.

Both the exterior unit and Inside system are the age of the house 1993.

I have a dual fuel system and my thermostat has an emergency heat.

This house thermostat did not have an emergency heat.

My set point is 30 degrees.

How does this heat pump system know how to differentiate from gas to electric?

Like I stated not seen a set up like this!!


I can not tell from afar there are so many variations on how a system can be wired with different controls to perform different functions.
The emergency on the stat is to be used if the outside unit fails the normal operation can and does bring the gas unit on if needed and during the defrost defrost cycle. Did you try to run the stat up 3 or 4 degrees above its setting and see if the gas kicks in. You may have a improperly installed stat but on the other hand depending on its wiring if the outside unit failed the gas furnace auto picks up the load. Sorry not much help from afar just to many variables

The gas ran fine, it was the heat pump mode I was questioning.

I understand, you need to be there!!

Thanks for trying to help me!!

Did you try to run in normal heat and just move the stat 1 degree to see if the heat pump operated with out the gas furnace.

It is possible someone just using the heat pump as standard A/C one could tell this by the amount of control wires traveling to the exterior unit from the furnace. It there are only two low voltage wires it is for cooling only if more than two wires it is used as a heat pump

There is like an entire electrical service meter on the outside (without the glass dome) in addition to the typical exterior disconnect.

It was a different set up then I am used to. Pic of exterior components on original post.

Why do you need an emergency heat setting on the thermostat?

If you want one. Change the thermostat. It does not effect the operation of the unit.

It does on mine!!