Furnace wil not come on with Living room T-stat anymore - HELP !!

[seandmelissad]

We have a 2017 4200 with 3 - ac units 15K each and the Suburban 35-SFQ furnace. What use to happen up until 12-4-2017 is this;

The T-Stat in the hall would be set to "Auto" and the temp set to 83 the furnace would kick the blower on and heat would come out of the floor registers. When this would happen a single tick could be heard in the area of the AC filter. Now what happens is the T-stat is set to "Auto" and the temp set to 83 and no blower / no heat. Just before this stopped the ticking sound in the AC filter area repeated itself many times.

If I go to the bedroom and turn the T-stat to auto and 83 degrees the furnace blower comes on and heat comes out. So this tells me the furnace is working.

I have called Heartland

I have called Dometic

I have swapped and reset the T-stats in the rooms and have changed the relay boxes in the AC units that control the furnace power from the Bedroom AC unit. I have pulled to cover to the furnace off and looked at the PCB and even turned the switch on the Furnace off and back on. To no avail the only way to get the heater to come on is from the bedroom T-stat.

Any help would be greatly appreciated.

Thanks,
Sean.

 

[danemayer]

Re: Furnace wil not come on Living room T-stat anymore - HELP !!

Only one thermostat controls the furnace. That's normal. Sometimes it's the bedroom thermostat.

What doesn't make sense is that it ever worked on a different thermostat.

 

[seandmelissad]

Re: Furnace wil not come on Living room T-stat anymore - HELP !!

Only one thermostat controls the furnace. That's normal. Sometimes it's the bedroom thermostat.

What doesn't make sense is that it ever worked on a different thermostat.

Correct. I called and talked with Heartland. They said per the build sheet the mid-ship T-stat and relay box was wired in series to the Furnace and that either can / does control the Furnace. The interesting part is that all of sudden the relay box that is in the AC filter wiring tick'd multiple times and then now the T-stat control in the living room with not kick the furnace on. We were able to get with some co-campers that have the same Cyclone and theirs is the same way and works.

Thoughts?

 

[danemayer]

Re: Furnace wil not come on Living room T-stat anymore - HELP !!

Correct. I called and talked with Heartland. They said per the build sheet the mid-ship T-stat and relay box was wired in series to the Furnace and that either can / does control the Furnace. The interesting part is that all of sudden the relay box that is in the AC filter wiring tick'd multiple times and then now the T-stat control in the living room with not kick the furnace on. We were able to get with some co-campers that have the same Cyclone and theirs is the same way and works.

Thoughts?

First I've heard of wiring multiple thermostats to control the furnace. I think the thermostat signals the control box in the ceiling to fire a relay and send 12V DC to the furnace. Ticking noise sounds like the relay isn't firing reliably.

Since you've already swapped thermostats without any effect, the problem may be where the wires come together - wherever that might be. Maybe they come together at the control box. Maybe on the way to the control box.