Duo-Therm/Dometic Air Con out- Hisense in.

[phantomjock]

{2008 Chevy 2500 170P}

Finishing up the effort, then comes the documentation. I'll use this thread to post all the photos of the effort, lessons learned, ideas.

The Window AC unit has a remote and I have no need for the Duo-Therm Thermostat to control it. Some of the wires remaining may serve some future purpose - perhaps. And, I've also pulled a set of 4 wire from the upper station where the Dometic resided to the Power Panel in the cabin. I plan to join these to provide the signal to the thermostat.

I plan on replacing the Duo-Therm thermostat with one of the 2 wire digital units other folks here on the forum have used (something that is AAA battery powered). All I want to do at the thermostat is operate the Suburban Propane Furnace. I will do this in 2 steps. First, using the Duo-Therm thermostat in place. Then, purchase and replace with an appropriate digital, 2 wire programmable thermostat.

Which 2 wires will I need?
1. Which ones on the Duo-Therm panel signal the Furnace?
2. Where can I find the 2 blue wires for the furnace?

There are supposed to be two (2) blue wires to make relay to the furnace.



But at the duo-therm not so.



The schematic at the furnace shows:



At the thermostat - I suspect the WHITE and the BLUE are the 2 signal wires I am looking to use to signal a start of the furnace - but, I am loathe to let the "magic Smoke" out until I've asked the questions:
1. Which ones on the duo-therm thermostat panel are for the Furnace?
2. Where can I find the 2 blue wires for the furnace? Power Panel area? Water heater space? At the Furnace - obviously, but a long way to go.

Advise and suggestions welcome.

Thanks in advance.

Cheers - Jim

[dicktill]

PJ - IIRC, the two wires for the furnace just need to be connected together; there is a separate supply of power directly to the furnace.

[TX-Trek]

Jim, I think you're familiar with the AC install thread that I did for our 210P, look towards the end and you'll see what I did for the furnace.

https://www.classbforum.com/forums/f...out-11478.html

The wiring at the original thermostat was powered and routed through the Dometic unit, and in our van there's no direct wiring to the furnace from the thermostat. I left that thermostat in place and traced the wiring from the old multi-pin plug left after the Dometic removal, and found the 2 wires going back to the furnace. As mentioned the furnace already has a 12v supply.
The 2 wires to the furnace simply complete the "on" circuit, and a thermostat just controls when that circuit is complete. I used a very simple non-digital thermostat, but of course a digital version can be used, just needs battery power. In my case there was a furnace control board issue that I verified after checking sail switch, high limit switch etc. I installed a Dinosaur Electronics replacement board.

We've used both AC and heat since the install with no issues at all, and interior temps have been well maintained.

[phantomjock]

Originally Posted by TX-Trek

Jim, I think you're familiar with the AC install thread that I did for our 210P, look towards the end and you'll see what I did for the furnace.

https://www.classbforum.com/forums/f...out-11478.html

YES - very comprehensive and useful. Thanks for sharing that. I am hoping to add a few bits of info on this thread from my experience too. Different unit and in a 170P.

The wiring at the original thermostat was powered and routed through the Dometic unit, and in our van there's no direct wiring to the furnace from the thermostat. I left that thermostat in place and traced the wiring from the old multi-pin plug left after the Dometic removal,

I figured the Dometic board was used as the junction for the furnace to thermostat wiring. The schematic shows it, but ground truth is useful. Thanks for the confirmation!

...and found the 2 wires going back to the furnace. As mentioned the furnace already has a 12v supply.

Where did you "find" those? I guess near the power panel/Tripp-Lite area? Would seem logical as that is where the Dometic gets its power.

The 2 wires to the furnace simply complete the "on" circuit, and a thermostat just controls when that circuit is complete. I used a very simple non-digital thermostat, but of course a digital version can be used, just needs battery power.

I'm leaning to the digital + AAA just to have the cabin temp visible.

We've used both AC and heat since the install with no issues at all, and interior temps have been well maintained.

I have done a couple of short "runs" of the AirCon (using the garage 20A circuit) when I'm inside the van working on the cleanup of the project. It is QUIET and cold! looking to do a test on the LiFePO bank to check energy consumption.

I'll be reporting and posting here. TX-Trek, Thanks heaps!

Cheers - Jim

[TX-Trek]

Glad to help, feel free to use the thread however you may need.

"Where did you "find" those? I guess near the power panel/Tripp-Lite area? Would seem logical as that is where the Dometic gets its power."

No, the 2 wires were located up by the rear shelf, within the multi-pin plug that used to attach to the Dometic. I pulled the furnace and found 4 wires - one constant 12v, one ground, and 2 green wires that were from the Dometic control board NOT the wall thermostat. There's no direct connection from the wall thermostat to the furnace once the Dometic is removed. In our van, the coach control panel has a fuse for that 12v supply to the furnace and a 110v breaker for the ac.

I checked for continuity to verify where the green wires went and found them routed to the multi-pin plug. I then removed the wires from the plug and tied in my new thermostat. As mentioned, they (and any thermostat) are just to close the circuit at the furnace. The AC install thread shows the additional wire lengths I added inside the upper cabinet in order to mount the new thermostat at my preferred location. Incidentally, that location seems to work well in providing a fairly uniform heat temperature throughout the van. The AC has a remote with thermostat, so that of course works independently from the heat.

I'd be interested to read how your final install works - in our case its been about 3 years now and I would do it again in a heartbeat. Very pleased with performance and reasonable replacement cost.