Using Atwood 1H2C Thermostat with Dometic A/C ??

[BillMartin]

I am attempting to replace a Duo-Therm Thermostat Model# 3107612.008 with an Atwood Model# 1H2C. Neither the furnace, A/C compressor, or A/C fan will operate with the Atwood. All functions are good with the Duo-Therm.

The Atwood documentation claims that it "has been designed to operate standard air conditioning units in conjunction with an RV furnace".

Furnace: Atwood Model# 8535IVDCLP
A/C: Dometic Model# 620426.331

Duo-Therm Thermostat connections:
Terminal Wire
-------- ----
+7.5 Red
Cool Yel
Fur Wht
Fan Hi Blu
Fan Tan
Gnd Grn

Atwood Thermostat connections:
Terminal Wire
-------- ----
1) Gnd Grn
2) n/c
3) +12VDC Org (voltage verified)
4) +7.5VDC Red (voltage verified)
5) Compressor Yel
6) Fan Hi Blu
7) Fan Lo Tan
😎 Furnace Wht

1) The Orange wire in the thermostat cable was not used for the Duo-Therm thermostat installation, and was not connected at either end of the thermostat cable run. The Atwood thermostat requires a source of +12VDC. The Orange thermostat wire is now connected to a wire labeled "+12VDC" in the A/C wiring compartment. This "+12VDC" wire appears in a cable from the coach wiring, supplying the A/C unit. Have verified that the Orange thermostat wire is at +13.5VDC with respect to the Green ground wire. The Atwood thermostat display "powers up" upon connection of the Green and Orange wires. The Orange thermostat wire IS NOT connected to "CON 1" of the A/C controller, which apparently would be the case for a Heat-Pump / Heat-Strip application, which I do not have.

2) I note that all of the thermostat connections (with the exception of the added Orange +12VDC wire) connect directly to the A/C controller. The A/C controller provides a pair of terminals which connect to the furnace's thermostat circuit. The furnace does not connect directly to the thermostat.

3) Have experimented with the "heat" function with no thermostat connected to any wiring. The furnace goes "on" when the furnace "White" wire is connected to the ground "Green" wire.

4) Have experimented connecting to the Atwood t-stat all wires except the furnace "White" wire. The A/C compressor and A/C fan do not operate.

5) On the Atwood thermostat, there is an undocumented "dot" in the lower left corner of the display which appears to be a "Call" indicator. This appears to be functional, is "on" in "heat" mode with setpoint above room temperature, is "on" in "cool" mode with setpoint below room temperature, otherwise "off".

Does anyone have any ideas why the Atwood won't work?

[Fisherguy]

Really, what hapened? Earlier you said it was working, did you use the power or the ground?
Mine works fine using the ground, not the 7.5 volts.

[clarinet]

Hi! This is Clarinet. I never got my Lux thermostat to work properly. I contacted the Lux rep and he told that I should return the thermostat becauseit will no work in my application. A complete 180 from my original contact.

[Fisherguy]

I used the ground. His works too, I didn't ask him if he used the ground or the 7.5 volts, but I think most other threads for these other thermostats also used the ground.
For the switch I removed the circuit board to put the switch in the front piece then put the board back:

[bearwayne]

I'm glad you got your thermostat working! I'm curious though--did you end up using the +7.5 or Gnd?i think it's good to provide those details for folks who find this thread in the future. I wonder if Clarinet got his thermostat working.

[Fisherguy]

OK, got my Lux, wired up the switch but with my setup I need to have the LO and the HI connected to get the fan to come on high speed.
I know I've seen other people's wired up like this, always thought you should only have the HI or LOW connected but doing it that way my hi speed wouldn't work.

[bearwayne]

The Hunter was difficult to use. It would take several presses on the screen to change settings. The worse thing is that on multiple occasions, it turned on the heat continuously even though the thermostat was set to "System Off"! The reviews for the Hunter on Amazon are pretty bad!

I like that the Lux has an adjustable temp swing. I was looking on their website to see if it did. My Honeywell does not as far as I know. I like a temp swing of +/- 1degree F. Otherwise, I notice wider swings.

[Fisherguy]

What was wrong with your Hunter? With the Lux you can adjust the temp swing, not sure if they all allow that.

I've given up on the Atwood.

[bearwayne]

The point of my post about my Hunter install was to show the wiring diagram. The brand of thermostat does not matter--I think all home thermostats are similarly wired and I -think- the terminal names are pretty much standardized. There are tons of posts on here about analog thermostats with various RC AC systems. That's how I figured out how to install mine. Btw, that Hunter I installed was terrible--I replaced it with an inexpensive Honeywell (not all Hunter thermostats are bad, just the model I bought.)

[Fisherguy]

Interesting.

The link you posted was for a Hunter thermostat..?

I better contact Lux, lotsa other posts for the Hunter say you don't use the 7.5 volt wire and connect the ground as you say.

[bearwayne]

I was referring to the Lux.

[Fisherguy]

bearwayne wrote:
I looked at the wiring diagram of how I wired my thermostat and it is similar to what th Lux Tech told you EXCEPT I did not use the +7.5V and connected Rh/Rc to the GND (Green)wire from the control module. This correlates with what Chris Bryant said about having to take the relays to ground to activate. You might try that if what the Lux Tech said doesnt work.

In this thread is the diagram of how I connected my analog thermostat.

link

What kinda thermostat are you talking about? Chris was talking about the Atwood, Clarinet was talking about the Lux.

[bearwayne]

I looked at the wiring diagram of how I wired my thermostat and it is similar to what th Lux Tech told you EXCEPT I did not use the +7.5V and connected Rh/Rc to the GND (Green)wire from the control module. This correlates with what Chris Bryant said about having to take the relays to ground to activate. You might try that if what the Lux Tech said doesnt work.

In this thread is the diagram of how I connected my analog thermostat.

link

[Fisherguy]

Clarinet, got my Luxtoday, do you have a pic on the switch you installed?
You say you put it in the base of the unit but the base is angled on mine, curios to see how you did it.
Thanks

[clarinet]

I made one small error in my post. You do not use the ground wire. What you need to do is get a piece of 18 gauge thermostat wire and connect it from the "G" on the thermostat to the center/neutral pole on the rocker switch. By the way you can get the rocker switch from the GoRving parts catalog on line. Good luck. Saves a little bit of money.