New thermostat question?

A regular low voltage stat of any kind for furnace operation is basically a switch , line in - line out

Any stat that can operate a rv AC is somewhat similar , the discontinued attwood stat 2h2c has a jumper to change between the capability of operating a dometic or a colman AC , this is not the part of this in question

The 2h2c stat that runs the 1522 , 2334 , and 2540 2 stage furnaces where the 1522 refers to 15 as the low gas valve btu and 22 the high gv btu and same for the two large units seems totally different in that it has 12vdc positive and negative suppled to it and then one wire -blue - going to the dual controller that somehow changes with the mode switch between

low manual - high manual gas valve and fan ,

auto -where it changes to low or high based on a differential of set temp and read temp ,

and fan only high or low

I`m unclear how one wire does this , is it some kind of modulated signal ? I`d be tempted to put a meter on it but wouldnt want to accidentally screw up a working stat that I cant get a replacement for

Seems like once you figure it out you could at least run wires from the dual controller to a different stat with maybe relays

Its not good that this is not made any more , furnace or stat , I remember that attwood discontinued them before dometic bought them out , so not dometic`s fault

If someone could figure this out they would save folks a lot of greif and money

OK, just checking in... I'm not having good luck so far. There is no new old stock I can find on the web. I had a friend of mine who is an A/C heating guy look at it and tell me the problem is the two stage units. Mostly the heater. Even if we hook it up to work on low speed which he can do it will want to work on the two stage system. He's doing some research on his end and I'll see him at church tomorrow. The only dual stage thermostat I could find that actually says it's duel stage is this one. I don't have an electric heater in my A/C but he doesn't think it will be a problem. Of course the wiring harnesses are not present so we'll have to cut some wires which will void the return. I'm going to call Coleman on Monday and ask about this thermostat and I sent an email to Dometic requesting there help. But like said above they are going to want me to buy a new unit which I won't do.
https://www.campingworld.com/digital-two-stage-thermostat-heatcoolheat-pump-black-105762.html?cgid=inside-rv#q=thermostats&start=12&cgid=outside-rv%2Fair-conditioners-accessories%2Fthermostats

3 tons wrote:

mbloof wrote:
The thermostat on most RV furnaces is a simple two wire interface.

Just about any 2-wire thermostat will work as a replacement of the stock unit.


- Mark0.

Not so, my Atwood dual stage 15/22 uses 5 wires...

I think "most" was the operative word here. :)

- Mark0.

mbloof wrote:
The thermostat on most RV furnaces is a simple two wire interface.

Just about any 2-wire thermostat will work as a replacement of the stock unit.


- Mark0.

Not so, my Atwood dual stage 15/22 uses 5 wires...

Hey towpro if you can explain please
The attwood stats that where made for the 2 stage furnaces (no longer made) have three wires to them 12v + , 12v - , and th from furnace ,as shown in page 15 of second link and furnace wiring in page 13 going to dual control, how does that work with a normal low voltage stat with w and r wiring , how would that switch between low and high fan and low and high gas valve ,there must be a way to do it , but I dont see it . Also note on page 13 at the top it says =

An Excalibur 2-Stage furnace must use an
Atwood Digital Thermostat.

thats what I remember hearing when I put mine in that it would not operate with any other

OK, Thanks to all. I just happened to check back before going to bed. The unit has 6 wires coming from the wall all hooked into a board. 5 of the wires are tiny and multi colored and the 6th wire is larger and blue. It is a two stage heater and A/C. Yes it turns to a lower fan setting when close to temp. I will take pics tomorrow for all to see. Can someone remind me on how to post pics? This unit was recommended on amazon, Take it or leave it... I will call Coleman on Monday to see if this will do it. I hate dometic.
https://colemanmachac.com/coleman-mach-wall-thermostat-7330g3351/
Thanks again to all of you.

I really hate Dometic for killing Attwood so they can sell more dometic **** when you can't get attwood parts.

Here is manual for your 8900 page 11 top

It looks like your thermostat just connects 2 wires from heater to turn heater on. (it looks like both wires at thermostat are blue).

so if this is true, the stage 2 heat is triggered by the control board depending on how long the burner runs.

your thermostat may also control your AC, there is 2 wires your connecting together with your thermostat. easy to wire with a standard household thermostat.

the trick is that the AC might have 2 fan speeds. I have had to add a small toggle switch by drilling a small hole in thermostat to mount a small toggle switch that is wired to control the fan speed.

but in later years Attwood (and I am sure others) started using a 4 wire buss between the AC and thermostat.
That and RV heatpumps is where you start to have problems wiring home thermostats.

Here is another manual

see page 14 and 15 of this manual. it has complete pin out for your dual stage thermostat

you should be able to duplicate this with a home thermostat, but you will need to add a toggle "fan switch" so you can switch AC fan between low/high.
again, I do not see a 2 stage controller so this must be done by control board in furnace. I recall having one in a Titanium camper and it worked well.

Because I`m interested in this because I have a Attwood 2 stage furnace in my 5th as I said that I installed in 2015 , and had nothing else to do today , retired , I called Dometic who now owns attwood @574 264 2131 and asked what I would do if the furnace or stat was to go out and was told I would have to replace the furnace .Not good !

To be clear is your furnace the 2 stage type that in auto position will go into a lower fan and heat level if its within a few degrees of the stat setting ? Your stat looks like mine , its a Excalibur 8500 1V furnace . If so its run on 12v and it only works for that heater.

I saw a few of that type stats on e-bay and at one rv online store I guess might be old stock , or maybe it can be repaired by an electronic guru , its not a simple stat it has a circuit board and capacitors ....

Let us know what happens

Actually if its a two stage heater like the one I put in my 5th , that attwood no longer makes , that has both a two speed fan and operates at two levels of burner - btus also then it has a 12 volt stat and you cant use a regular home stat , or an rv stat like I put in my Lance TC
Call Attwood

Make sure it can be turned off , or to another mode like ac . Or the fan will run if the temp falls below the lowest temp setting .Or at least disconnect battery's when not used .