Gas Furnace runs while in cool mode... NEED HELP

[Rookie2012]

Today at one of my service calls, the customer stated that the AC wasn't working properly. When I went in attic, the furnace was operating while in cool mode. This is a duel fuel system with gas as the primary heat and the heat pump for emergency heat. I took off the wires at the control board and jumped R and Y and O and the furnace did not come on.I took wires off at the thermostat and I jumped R,Y,O furnace did not come on, I jumped R,Y and the furnace did not come on. I went outside to see if I was getting 24v to outside unit while t-stat was in cool mode. I was getting 24v from Y to common but outside unit wasnt coming on. The pressure switch had been cut and wire nutted together. I then jumped y( t-stat wire) straight to contactor and the outside unit came on in cool mode and in heat pump mode . So apparently I have a bad defrost board. However, the gas furnace still continued to run. I don't think its the board because I took W off of the board and the outside unit ran and the furnace didn't come on.I cannot figure out why the furnace runs while in cool mode or EM heat mode. My co-workers think its the thermostat or a short somewhere in the t-stat wire. I'm not totally convinced its the thermostat. I'm missing something. Any advice or troubleshooting tip would be helpful! Thanks

[jtrammel]

Why is the heat pump the emergency and the gas primary, sounds backwards to me. Sounds like something's messed up in the low volt wiring scheme

[Rookie2012]

Yea I plan on changing the primary heat to heat pump when I go back Thursday to replace defrost board.

[samejj]

when i get mess's like this i just gut the old wiring and start over the way it should be... most often its faster then figuring out what the last guy did and when you leave you'll know its right..... HO loves to hear " this is gonna be awhile ".

[Rookie2012]

Ok thanks samejj.

[Saturatedpsi]

This is a duel fuel system with gas as the primary heat and the heat pump for emergency heat.

I'm having some difficulty understanding how that was accomplished in the first place, with a typical heat pump stat and "dual fuel" accessory control.

[pacnw]

what thermostat?

how is it programmed?

how is dual fuel controlled?

why is pressure switch out of the loop?

[coltsfanatic]

If it was the high pressure switch disconnected, in heat mode wouldn't the head pressure get really high if you are running the gas furnace and heat pump lol?

[Bsmith816]

Just when you think you have seen it all, you run into something else. I've never seen the gas furnace primary with heat pump being the EH.
I did have that problem one time and what was happening I found the W touching Y inside the wall where they shot a nail through the wire when it was installed 15 yrs prior. I couldn't believe it ran for 15 yrs before finally showing

[HotWaterHeat]

when i get mess's like this i just gut the old wiring and start over the way it should be... most often its faster then figuring out what the last guy did and when you leave you'll know its right..... HO loves to hear " this is gonna be awhile ".

This is EXACTLY what I do every time.

(The bad part is that 9 out of 10 times it was my co-worker that wired it all screwed up to begin with)

[JEG8233]

I'd be willing to bet that the W wire going from T-stat to furnace is shorted. I had a service call a few weeks ago on a Trane furnace were that was the culprit. Good luck.