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Old 05-01-2015, 07:43 AM   #1
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Duo-Therm Analog Thermostat Problem?

Hey folks!

I'm getting ready to move fulltime into my RV next week! Trying to nail down what I think is a problem with my thermostat.

The A/C blows freezing cold, both fan speeds run, etc...., but I am not able to select Fan ON without the A/C being on.

Also, with the A/C on at colder temps, the fan runs continuously (AUTO selected) even when the compressor is cycling on an off, but at higher temps, the fan runs only when the compressor is on, as expected.

Does it sound like a faulty thermostat? Or miswired?
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Old 05-01-2015, 06:02 PM   #2
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Find the make and model of your thermostat, then Google for the manual. It should show wiring diagram and also explain how it's supposed to function. A more modern, computerized thermostat might also be something to consider, especially if you're going to full-time in the future. A thermostat that can control day/night temperature is something to think about. Just be sure a new thermostat is compatible with your A/C unit(s).
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Old 05-05-2015, 11:54 AM   #3
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Great idea to get a digital thermostat! I did some research and just got a Honeywell Programmable unit for $25 at Home Depot.

One challenge I have is that I'm half color blind so I'm not sure which wire to attach. I did read that I don't need the 7.5v wire since the thermostat is battery powered. Also that I should just use the wire for the high speed fan or to add a fan switch if I want both speeds.

Can anyone look at the pic and tell me please using the name of the Duo Therm wire (COOL, FUR, HI FAN, FAN, GND) and what it matches with the Honeywell letters (B, O, G, Y, W, R, RC)?

Thanks!

Ron. :-)
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Old 05-05-2015, 12:08 PM   #4
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There should be an instruction sheet or manual with the new thermostat that tells the function of each terminal. The batteries usually only power the clock/memory function of the thermostat. RV thermostats are usually 12 v, home thermostats are usually 24 v, not sure yours will be compatible. It must be hooked up to the 12 v so it can control your furnace and A/C.
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Old 05-05-2015, 12:13 PM   #5
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Looks like this is it....
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Old 05-05-2015, 12:20 PM   #6
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Mod #100: Honeywell Digital Thermostat
Mod #100: Honeywell, Dometic and Suburban Digitial Thermostat Install | ModMyRV

Mod Description:

This modification was designed and completed by ModMyRV member Lencactustwo. Credit given to Ken Lenger, Alan Paskey and Les Adams for their detailed instructions with their A/C, furnace and digital thermostats. Mine is like all others, slightly different with different wire colors and a Honeywell 5+2 digital. This article carries a copyright. Permission must be obtained from the author before duplication or reposting.

I purchased my unit at the HD for $25 and have seen same at Wally and Lowes for about the same. The switch I found at Radio Shack SPDT (single pole double terminal) but found out I just needed a switch SPST (on /off) for $3.50 as did Les Adams. A little tricky notch in the bottom right corner of the base and back panel to fit. I would do it again but on the left side due to projections on the back of the circuit board.

Mod Difficulty:

My wiring was as follows: yellow wire (always A/C) to Y. White wire to W (for the furnace). Basically all furnace wiring is power wire to white, touch your power wire to the white and presto the furnace starts and cycle thru for about a minute (hint- twist them together to keep you and your loved ones warm while you figure out what else to do) (another hint- twist the yellow and your power wire together to keep you cool headed instead of the furnace).

If you twisted the red wire (typical power) to the yellow or white wire and it did NOT start the A/C or furnace, then try either of them on all other wires until it does. THAT wire is the powered wire and will go on to the R or RC terminal. My case it was the green wire to R/RC with jumper in (u shaped wire between R and RC [furnace and cooling circuits]) Now both A/C and furnace have power when the switch on the bottom is on heat(R/RH) or cooling (RC). Brown wire to G (which runs the A/C fan).

NOW for the tricky part: ALSO put one side of the Radio Shack SPST (on/ off) switch wire into the G terminal and the other to the blue (high fan speed) wire. It works like a tri light bulb 50/100/150 watts, you need 50watt on and 100watt on to get to 150watt, so both wires are powered by the G terminal to get high fan speed, see diagram below that I modified from a Hunter diagram

Don’t worry about the red wire not hooking up, you probably found out it had no power on it, and as the other gentlemen installers noted DO NOT CUT the red wire short as you may need the wire one day for future mods or the buyer of your rig when you sell it down the road may want the old thermostat re-installed.

Remember both the Honeywell and Hunter thermostat instructions were designed for home use not RV use. I have personally installed them in homes and they are exactly as laid out in the instructions: red for power, white for heat, yellow for A/C and green for fan, EASY PEZZY. Us RVers have to follow other instructions!! You know, if they sold one to work in our rigs, it would be 3-4 times the price!

Follow any of the great mods for this UPGRADE to enjoy constant temperatures in your rig so you don’t have to hear “I’m cold…I’m hot”. YES it runs MORE often, but for SHORTER times and more accurately as you can see the digital readout in 1 degree increments, not “kinda between 10 and 20, half way, somewhere, maybe 17 ¼ degrees?” Press either the up/down arrow ONCE to light up the display without disturbing the program and press AGAIN while lit up to change settings for temporary comfort relief (2 hours) or touch RUN to go back to the scheduled settings at any time.
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Old 05-05-2015, 01:19 PM   #7
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DONE!

Works great! The schematic above matching Duo Therm names with Honeywell letters did the trick!

Bflinn, thanks again for the idea of the digital thermostat!

I think I will add a switch for the fan speed later.

Ron
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Old 04-17-2016, 04:33 PM   #8
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Honeywell wiring

I bought the Honeywell model rth 5100b
I hooked up wires according to forum with a switch for high and low
Red = power and capped off
White = furnace (landed on w ) of honeywell
Yellow = ac (landed on y) of honeywell
Brown or tan = fan (landed on g) of honeywell
Green = ground (landed on Rc and R ) of honeywell
Blue = fan hi (landed on one side of spst switch other side to g of honeywell)


I set the Honeywell to 1 / 1 on display for heat pump outside condenser sharing ac/heat

My problem is the heat or is always on. I switch honeywell to ac on and it turns on with the heat at same time. I turn on heat and it turns on.

why does the heat never turn of unless I switch breaker off

Please help would like to take kids camping
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Old 04-17-2016, 05:00 PM   #9
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shift10gears

What color wire for HP and where did you connect it?

T-stat Programing
Function 1----System Type (1) for HP
Function 2----HP Change-over valve ????? where is HP wire
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Old 04-17-2016, 11:46 PM   #10
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I didn't connect any hp wire.
maybe that's my problem, I set up the Honeywell wrong.
can you please help so this heater will shut off and I can take kids camping, thanks so much
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Old 04-19-2016, 12:22 AM   #11
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Quote:
Originally Posted by shift10gears View Post
I didn't connect any hp wire.
maybe that's my problem, I set up the Honeywell wrong.
can you please help so this heater will shut off and I can take kids camping, thanks so much
What was your OEM T-stat?

A Duo-therm, Atwood/RVP, Coleman etc.
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Old 04-19-2016, 08:17 PM   #12
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I have a duo therm exactly like picture on this post
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Old 04-19-2016, 08:40 PM   #13
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shift10gears, with the old thermostat, how did you select between A/C and Heat pump? There is a changeover valve in the rooftop unit that switches from heat to A/C. According to the manual, pg 14,

https://customer.honeywell.com/resou.../69-2329EF.pdf

A wire labeled 'O' or 'B' should have been present in the old thermostat. (Unless the changeover valve is controlled in a different location) That wire should be connected to post 'W' and the appropriate program setting must be selected.

The linked article about changing over to the digital thermostat is good, but it doesn't mention a heat pump and furnace, just an A/C and furnace. No mention is made about hooking up a heat pump (heat and A/C) and a furnace. That's probably why your unit is stuck on one mode, the changeover valve wire needs to be found, connected, and program settings made.
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Old 04-19-2016, 11:45 PM   #14
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my duo therm looks exactly like the first thumbnail pic of this post

I bought the Honeywell model rth 5100b
I hooked up wires according to forum with a switch for high and low


duo therm wires Honeywell wires

Red = power and capped off
White = furnace (landed on w ) of honeywell
Yellow = ac (landed on y) of honeywell
Brown or tan = fan (landed on g) of honeywell
Green = ground (landed on Rc and R ) of honeywell
Blue = fan hi (landed on one side of spst switch
other side to g of honeywell)


I don't have a heat pump wire and the old duo therm hp doesn't have a spot for a wire.
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