Wiring thermostat to run fan for heat exchanger instead of trying to run propane.

[Cmaxwell0569]

So I have a Coleman LP/NG furnace/AC model number is FC35CXC1A hooked to a Pro1 T701 thermostat. The propane portion of the furnace hasn't worked since we bought the house in 2021 (no tank, the line is gone, they basically never hooked the propane side of it up) we brought our outdoor wood boiler and heat exchanger from the old house with us and are trying to get it all set up finally after finishing the rest of the upgrades the new house needed. My issue is figuring out how to wire the thermostat so that when the house temp drops below the set temp it will turn the fan on to use the heat exchanger instead of the furnace trying to run the propane and still be able to use the same thermostat during the summer by using the "heat/off/ac" switch. Currently we have been just turning the thermostats fan switch to "on" when heat is needed and off when it got warm enough but that has led to us coming home/waking up to a cold house. Would like to keep it limited to just the one thermostat for the blower motor and ac if possible. Any and all advice is appriciated as all our "local" (we arent local closest town is 50 minutes away) hvac companies are booked out for at least 3 weeks and even then I've been informed with where we live it will be a minimum of $150 for them to send someone out not including labor once they get here. Pictures of the thermostat are attatched below. Thanks again

 

[gthomas785]

Add a jumper from W to G

 

[sloeffle]

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[hedge wood]

Add a jumper from W to G

This will do what you want. On my Garn set up I have a heat exchanger's in three LP furnaces. I have mine set up so the LP can be used any time not that I do unless the Garn starts to leak again. I have two thermostats on each floor of my house for each furnace. One runs the AC and LP. The other one runs the Garn. I turn my pumps, furnace blower on and off as needed to maintain the set temp. I have a relay in each furnace that when heat is called it puts power to the G terminal to start the fan. I like mine having two system so if something happens to me the Garn can be shut off and the LP can be turned on. The basic LUX thermostats are cheap. I run the Ranco's out in my shop for the floor heat and my LP furnace and heat exchanger in the furnace. I currently don't even have a tank out there hooked up.

 

[Cmaxwell0569]

Add a jumper from W to G

So just run an additional wire from W to G? I was confused as reading other forums they said it would turn the ac on doing that?

 

[gthomas785]

So just run an additional wire from W to G? I was confused as reading other forums they said it would turn the ac on doing that?

It shouldn't if it's wired correctly.

Typically Red is the 24v power, connecting it to White will call for heat, connecting it to Yellow will bring on the AC, and connecting it to Green will bring on the fan. That's all the thermostat is doing when it controls the system.

You could just move the green wire over to W. But that would disable the fan "on/auto" switch from working so better to use a jumper effectively connecting the green wire to both W and G.

And since you're not using the LP heat, you could also disconnect the white wire to prevent it from calling on the furnace to heat up.