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]

THanks, if I can't get this thing to work that will be something to think about, 17 bucks and backlit seems like a bargain compared to this Atwood POS.

[clarinet]

Yes, exactly. Here's what I got for directions. (copy of email)
Converting from Dometic Analog thermostat. The wiring is as follows:
Red is 7.5v
Black is Cool
White is Furnace
Blue is Hi Fan
Orange is Low Fan
Green is Ground

LUX wrote:


Wire the DMH110c as follows:



Red / 7.5 dc = Rh w/jumper to Rc

Black / Cool = Y

White / Furnace = W

Blue / Hi Fan = G (usually used in cooling mode)

Orange / Low Fan = G (usually used in heat mode)

You would have to manually change the Lo & Hi speed wires to the “G” terminal to control multiple fan speeds. Our unit has only 1 G/Fan speed terminal.

Green / Ground = TAPE OFF, Do Not Use.



Joel-Tech 856-234-8803 x 7


My additional notes for fan speeds: I used a SPDT rocker switch and cut out a piece from thermostat mounting plate.
Take Green/Ground attach to to neutral pole on switch then connected hi fan to one pole and low fan to other pole.




Thermostat model number

DMH 110c

Message

[Fisherguy]

clarinet wrote:
I gave up an returned the Atwood 1H2C thermostat for credit. I am going to install a LUX DMH110a thermostat and adding a single pole double throw (SPDT) switch. It's the simplest install and have great support from LUX.

One of these?
LUX


How'd you figure out how to wire it?

[clarinet]

I gave up an returned the Atwood 1H2C thermostat for credit. I am going to install a LUX DMH110a thermostat and adding a single pole double throw (SPDT) switch. It's the simplest install and have great support from LUX.

[Fisherguy]

Chris Bryant wrote:
On that diagram they hook up #2, with nothing on #4, they also list #2 (and the black out of the control box) as both +7.5 *and* ground. I wish I knew what terminal 2 actually was- terminal 4 they list as relay common, which makes sense- on a standard t-stat that would be terminal R (C or H).

Tried that today, set it to AC and what do you know the AC came on, I could also change the fan speed, HI or LO, only thing is it would not turn off when my set temp was lower than the current temp, and the furnace didn't come on at all.

Will contact tech support again tomorrow.
How can they sell these things for more than the Dometic is beyond me ...?

[Fisherguy]

These Atwood thermostats are not cheap, the instructions suck.
For less money someone could buy the Dometic thermostat that includes the parts for the Dometic AC unit, bet Atwood doesn't sell a lot of these.

My bud gave the Atwood to me after he gave up on trying to make it work, he put the Dometic in and had absolutely no problems with the install.

Removing the board from the unit and turning it over, looks like it was made by Channel Products Inc.

[Chris_Bryant]

On that diagram they hook up #2, with nothing on #4, they also list #2 (and the black out of the control box) as both +7.5 *and* ground. I wish I knew what terminal 2 actually was- terminal 4 they list as relay common, which makes sense- on a standard t-stat that would be terminal R (C or H).

[Fisherguy]

We're leaving for a trip in 2 days, I don't think I'll have time to try it with 2 jumpered to 4, maybe I'll take it woth me on the trip and play with it while away.

One of the Atwood techs sent me this when I was trying to get it to work.

[Chris_Bryant]

Really, the only relay that could click without activating something would be the high/low fan relay- the compressor and fan relay should run those if they click.
They simply do not give enough info on operation, so I don't know what terminal 2 is on the t-stat.

[Fisherguy]

OK, so would that be why I heard relays clicking but nothing out of the AC or furnace?

Interesting page 14 is dated 6/19/02 and the instructions that came with the unit (and the one I linked to above) are dated 9/21/04, they're newer, you'd think the newer ones were correct...?

[Chris_Bryant]

Further proof that Atwood is relatively clueless- see page 14 of the service manual, which gives the instructions I gave.
No- I haven't dealt with one of these.

[Fisherguy]

clarinet wrote:
How do you install the new 12 volt wire?

To test it I jumpered to a light fixture near the thermostat, if it worked I was going to try fishing the ceiling and the wall by removing the trim around a roof vent to help run the wire.

Chris Bryant wrote:
Atwood's instructions say to hook the +7.5 (red) to 2 & 4. I still think Atwood doesn't know how the Dometic analog system works, though- they need to switch the grounds to activate any relays.

Not from what I can see:

Atwood Instructions

Have you actually installed one of these and been successful? Dometic AC and Suburban furnace?

[Chris_Bryant]

Atwood's instructions say to hook the +7.5 (red) to 2 & 4. I still think Atwood doesn't know how the Dometic analog system works, though- they need to switch the grounds to activate any relays.
It would really help if they used anything close to standard terminology with this.

[clarinet]

How do you install the new 12 volt wire?

[Fisherguy]

No, Chris' suggestion didn't work, neither did running a new power source, I could hear relays clicking but nothing from the furnace or ac.
My bud gave me the thermostat after he tried it and also couldn't get it to work. He's looking for his receipt, if he finds it I'll see if I can get a new one.

Here's the way the Atwood tech told me to wire it.
Blue from duo therm hi fan to Atwood 6
White from duo therm furnace to Atwood 8
Yellow from duo therm cool to Atwood 5
Brown from duo therm fan to Atwood 7
Red from Atwood 7.5 volt to Atwood 2
Ground to Atwood 2
New 12 volt to Atwood 3

Would like to get it to work but will be leaving for 3 weeks on Thursday, put the old duo therm back and it works fine.