Furnace not working

[JackMS]

My furnace will not come on at all. It is an Atwood 8535IVDCLP. I found the procedure to bypass the thermostat and it works when I do that. So I was about to order a new thermostat but I got thinking.

The thermostat is a dometic 5 button. I replaced the front a/c heat pump about 3 years ago and I had to order an additional circuit board to swap out on the unit to make it work with my thermostat. Both a/c's are dometic penguins. I think I used the furnace since then but am not absolutely positive of that. Is there anything on the roof a/c I should check first or is it most likely the thermostat? If the thermostat is the issue, would I be better ordering the updated thermostat and putting the original board back in the front a/c? Or is it even possible since the rear a/c is the original 2005 model?

I know a lot of questions but I know there are a lot of very experienced a/c guys here. Thanks in advance.

[enblethen]

Just wanted to verify that it was on different zone.
Could be a simple as loose connection on control box or splice at that location.

[JackMS]

Zone 2 does not show furnace, as it never has. A/C and heat pump work normal front and rear.

[enblethen]

Did you try Zone 2 for furnace?
The telephone line sends signal to control box. If other functions are working, the problem is at the control box or in it.

[JackMS]

enblethen wrote:
Have you verified that the thermostat is set for heat in the Zone that has the furnace connected?

Yes. Zone 1 said "furnace" I turned temp way up.

ppine- you are correct- Pulled the thermostat off the wall and all it has is a telephone style cord. I have some schematics so hopefully can get this figured out.

[ppine]

The appliances in RVs are not like the ones in a house. This has been a source of frustration for me on several occasions. I have found that RV mechanics, including the mobile ones can fix problems very quickly for not much money. Often it is dirt in an orifice or something simple.

[enblethen]

It would be in the roof top unit.
The thermostat transmits a signal to this unit.
Have you verified that the thermostat is set for heat in the Zone that has the furnace connected?

[JackMS]

enblethen wrote:

Looks like contacts are in control unit.

When you say "control unit" are you talking about the Comfort Control center inside the coach, which I think most people call the thermostat, or are you referring to the circuitry in the roof top heat pump? I haven't been on the roof yet but it seems so far that the contacts controlling the furnace are not closing since the test I did jumping the 2 blue wires at the furnace made the furnace come on. So if I go on the roof and one blue wire has 12 volts and the other never gets 12 volts, that will reaffirm that the contacts are not closing. But then we are back to are the contacts/relay bad or is the relay not being told to close.

Once I get the roof top unit open and get my memory refreshed I will know a lot more. Thanks for the help everyone.

[enblethen]

Not sure about wiring of your system, but some have a relay to prevent the AC from operating at the same time furnace.
Furnace should provide it's own power and relies on a contact closure for operation from the thermostat.
Looks like contacts are in control unit. Have you checked the mode functions in the zone for furnace operation?
From manual:
If a furnace is operated by the Comfort Control Center, the thermostat wires are attached to the two (2) blue wires from the control box. The furnace dip switch for that zone (control box or power module) is turned on

[JackMS]

I did that and furnace came on and made heat. So my next step will be to see if that power is getting to the a/c circuit board and coming back out of it.

[enblethen]

You can jumper the blue wires at the furnace.

[JackMS]

Thanks Doug. I'll go on the roof when the rain stops. One of the blue wires at the furnace has power and when jumped together there, the furnace works. But of course that does not mean the power is making it up to the roof.

[dougrainer]

If the furnace "shows" on the tstat, it has the correct DIP switch turned on for the furnace. BUT, if the furnace is malfunctioning or the furnace FUSE is blown it will not operate. It will still show furnace on the CCC if the furnace fuse is blown.
Unless you REPLACE the other AC/HP, you cannot use the new CCC after replacing the new board in the new Penguin. 5 button and 10 button control boards are not compatible and your rear penguin would not have worked with the 5 button system if it had the 10 button board. Doug

PS as I explained, you have a FURNACE problem , not a Dometic control problem. If you want to take the time, go up to the Front Penguin board. The 2 BLUE wires on the board are the furnace wires. Jump them together. IF the furnace does NOT come ON, you have a furnace problem. Also, 1 of those 2 blue wires should have 12 volts from the furnace. IF you have NO 12 volts on either blue wire, you have a furnace problem.

[JackMS]

It is a Duo-therm 5 button Comfort Control unit. I haven't done a reset yet. I am sort of under the impression that if the a/c's and heat pumps work and "furnace" shows on the thermostat that it doesn't need to be reset. But I could be wrong.

[enblethen]

What is make and model of thermostat?
Have you tried resetting the thermostat? Procedure varies with different makes and models.

[JackMS]

Thanks for the links. The furnace shows on the thermostat. It's just when I select furnace and adjust up to 80 degrees(it's 60 out right now), nothing happens. This all started a few weeks ago when it was 40 out and I needed it but it wouldn't come on. Luckily, it was warm enough that the heat pumps still worked good.

I'll read through the links and see what I can figure out