Replacing a duo-therm thermostat with a Nest E

[Merlin80232]

Has anyone replaced their duo-therm with a nest thermostat? I have 6 wires, red, yellow, white, blue, orange and green in that order. I just need to know what color wire goes in which slot (Y1, G, R, W1, C and OB).

[Bama Rambler]

Can you post a picture of the existing thermostat?
Also take a pic of the wiring on the existing t-stat.

Be aware that in some cases the Nest needs a "C" wire which you don't have.

[Merlin80232]

Yes

[brad8938]

A couple of things I see:

Like previously mentioned. You don't have a common wire (C). In my past experiences this might cause some issues. Most smart thermostats require a C. Not sure about a Nest but my Ecobee does. A few of my friends which have Nest had to rerun their t-stat wires to allow for a Common wire. They ran into an issue where the compressors in their condensing units started to act unsatisfactory.

You have two fan wires (typically your G terminal and green wire). I bet one is for the furnace fan and one is for the AC fan or one could be for High Speed and the other for Low Speed. Again, not sure about the Nest but don't recall seeing a setting to allow that for on the Ecobee.

[Merlin80232]

I was chatting with tech support last night and she kept telling me she needed to know how the wires were coming off of the “hvac “ unit. I told her that I didn’t even know where it was! Lol

[jimmarako]

OK, I'm going to pretend I know what I'm talking about. I am not an HVAC tech or even in the field, just a weekend warrior.

The picture below shows your typical HOME setup with 5 wires going to the thermostat. Also notice that the furnace/air handler/AC is the basically "one" unit. This is why the women at tech support wanted to know what was coming off your HVAC unit. These go to one spot in the house. But they go to two different spots in the trailer.

Looking at your setup you got three wires correct: Red (hot), white (Heat) and Yellow (AC). For you Green would be common, usually its Fan. Your Blue and Orange wires are for AC Fan. The Furnace Fan will come on when heat is called for. You could hook one of these Blue/Orange wires to FAN but that may not work. The typical home air handler will turn on the Fan to one of two speeds automatically when Heat/AC is called for. The Fan wire is typically only powered when you flip the "FAN ON" switch on the Tstat.

Besides the wire not quite being right I wonder. Typical heating systems are 24V AC. Our trailers are 12V DC. And if your thermostat is correctly labeled yours might be 7.5V DC. You would need to check if the Nest will run on other than 24V AC.

My 2 cents: I know people want to trash the Analog Tstats in the trailers. Even though I have a Nest at home I don't see the need for anything other than a basic one/off switch (analog Tstat) for a shoe box sized trailer. Just me being lazy/cheap.

There are other threads on upgrading the Thermostat. Getting a digital version of your current one is the easiest way upgrade. You can use a typical battery powered home Tstat since they don't need AC voltage or a common to run.

Good luck if you choose to get the Nest E installed. You'll definitely need to spend more time with tech support.

Jim M.

[Merlin80232]

Great info! Thank you all for your input. I will contact tech support again tomorrow with this updated information.

So I may sound like an anal dork, but the biggest reasons I wanted to go digital rather than analog is because I want to be able to set precise temps and control time of day temps.

I had a nest at my old place and I was very happy with the decrease in my utility bill.

Thanks again!

[itat]

If you aren’t looking to be able to see and control the temp remotely, I recommend you get a much less expensive digital, programmable thermostat that uses AA or AAA batteries. That’s what most people use to replace those old style analog thermostats.

[Merlin80232]

The problem is I have already purchased the nest thermostat

[Steve-W]

The nest will only work with a 24 volt ac system. You can make it work in your trailer but you will need to power it from 120VAC using a step down transformer to 24VAC and use relays to control your trailers AC system and furnace. It can be done but will take a bit of work to make it happen. You will loose the 2 speed fan unless you add a manual switch to go between hi and low fan speed. You will also loose the ability to run your LP furnace without shore or generator power available.

I highly doubt that Nest tech support will be willing or able to help you with this as it is a non supported use from their standpoint.

[Merlin80232]

After all of y’all’s input... does anyone want to buy a nest for their home? Ha! My 5th wheel is now my full time residence.

[Merlin80232]

Is there a programmable thermostat that will work in my trailer? Do any of you use one?

[Steve-W]

Originally Posted by Merlin80232

Is there a programmable thermostat that will work in my trailer? Do any of you use one?

Many will work. What you need to look for is a stat that runs off battery and does NOT require a “C” wire from the HVAC system. The wiring will be simple to swap. Two things you will not be connected. 1- the 7.5 wire on the left, be sure to insulate this wire as you do not want it to contact anything. 2- you will either need to choose Lo or Hi fan speed and connect that to the fan terminal on the new stat. Again insulate the unused wire.

You can add a manual switch to go between Lo & Hi if you choose.

[Chuck_S]

I've been using a Hunter battery powered thermostat in my Roo for both the furnace and AC unit. <--- that's a link.

Here's how to wire it. Probably works for similar thermostats. Note to get both AC speeds requires wiring a little switch into the unit.

Hunter Thermostat

-- Chuck

[Bama Rambler]

To summarize some of the things you need to be aware of when changing the Dometic analog thermostat.
1) Dometic switches the negative side of the circuit instead of the positive like most other systems.
2) You need a replacement thermostat that runs on batteries (usually AA or AAA) because residential hvac systems run on 24 vac.
3) Because of #1 you don't need to use the positive wire. You will use the negative (ground) wire under the R/Rc terminal of the replacement thermostat.
4) Dometic does their fan speed weird. In order to get High speed you need both low and high relays powered, so you have to tie the wires together at the thermostat to get high speed. You either put them under the same terminal for high speed only or you break the high speed wire through a mini switch in order to be able to choose between high and low.

[nayther]

Originally Posted by Bama Rambler

To summarize some of the things you need to be aware of when changing the Dometic analog thermostat.
1) Dometic switches the negative side of the circuit instead of the positive like most other systems.
2) You need a replacement thermostat that runs on batteries (usually AA or AAA) because residential hvac systems run on 24 vac.
3) Because of #1 you don't need to use the positive wire. You will use the negative (ground) wire under the R/Rc terminal of the replacement thermostat.
4) Dometic does their fan speed weird. In order to get High speed you need both low and high relays powered, so you have to tie the wires together at the thermostat to get high speed. You either put them under the same terminal for high speed only or you break the high speed wire through a mini switch in order to be able to choose between high and low.

Being a HVAC professional I can tell you Bama Rambler has it right on the head. And the nest won't work. It utilizes a capacitor for temp. power if you lose 24 volts, not to keep it powered.

[Merlin80232]

Thank you all for your input! I am still looking. Any opinion on the most efficient brand/model?

[JPin AZ]

I have been thinking about the one in this video to replace mine.

https://www.youtube.com/watch?v=6CPtV_iX9GQ