Wiring for replacing A/C thermostat are confusing - please help

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
K

kimmers39

New member
Joined
Jun 9, 2018
Posts
2
Good evening.  I have an old TS Express 5th wheel, the furnace and A/C are on separate thermostat controls.  I would like to replace the old Duo-Therm (Dometic) with a Honeywell programmable.  The problem is the wiring, not sure what they did here previously, and I can't find a manual for the RV, the original owner is deceased.
The Duo-Therm is wired as follows

Red wire connects to the connection labeled (+12)
Yellow wire connects to the connection labeled "cool"
Blue wire connects to the connection labeled "Hi fan"
Orange connects to the connection labeled "Fan"
White wire is connected to the connection labeled "GND"

The Honeywell of course has connection options for B 0 G Y W NOT USED R & RC

I "think" I need to cap off the red wire as I am permanent and do not use 12V, and the thermostat doesn't have a 12V connection anyway.
The Orange & Blue wires can connect together in the G terminal
White should connect to the RC terminal
Yellow goes to the Y terminal

Does this sound right???? 
 
The thermostat needs the +12v for power to operate. It also uses 12v to signal the furnace and a/c to heat or cool.  Residential thermostats are 24v, but they usually run ok on 12v. I think the R terminal is power for the Honeywell.

By the way, your RV uses 12v extensively, whether on shore power or not. The lighting, for example, and the circuits board for the appliances.
 
There isn't even a battery installed in the RV to run 12V.  I thought the R & RC were grounds?
 
It depends on which duo therm setup you have, if it dates back to before about 2003 this should work.  See https://www.youtube.com/watch?v=RFmyzGhHIgw  note this style of duotherm / dometic thermostats did not use 12VDC  they used 7.5VDC, though there was another similar style that I think used 12VDC.

p.s. there are other similar write ups like this one http://www.rverscorner.com/hunterstat.htm that include adding a hi/lo fan switch
 
I don't know if you plan on towing, but if you do you will need to reinstall the battery as it is used to power the brakes in a breakaway situation.

Ernie
 
There isn't even a battery installed in the RV to run 12V.
Click to expand...
It doesn't need one.  It has a 12v converter that generates 12vdc from 120vac shore power. The battery is used only when no shore power is present to operate the converter.

Thermostat R, RC and RH are "hot" terminals, i.e. power rather than ground.  R is a simple hot wire, while RC is for cooling function (a/c). Some also have an RH, for the heating function.  The wire for the R terminal is typically red, but there is no official standard requiring that.  Typically in a single wire hook-up, the R terminal is jumpered to RC to provide power to both terminals.  The ground is called the C or Common wire.  You didn't mention the Honeywell model, but usually this sort of thing is covered in the installation instructions.

This article may help somewhat. It shows the typical 24v residential wiring for R & RC, but 12v from the RVs power system is usually often sufficient.
https://diy.stackexchange.com/questions/63039/on-a-thermostat-are-r-and-rh-terminals-the-same-thing

And these also:
https://www.thermostatcenter.com/thermostat-wiring/
https://diyhousehelp.com/how-to/honeywell-4-and-5-wire-thermostat-wiring-instructions
 
You must log in or register to reply here.

Latest posts

Members online

Total: 1,166 (members: 36, guests: 1,130)

Forum statistics

Threads
131,984
Posts
1,388,644
Members
137,733
Latest member
[email protected] Ke
Back
Top Bottom