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Old 01-05-2011, 02:39 PM   #1
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Duo-Therm voltage; measurement & draw of

I've searched and read on several of the "conversion" threads (in these forums and others) in doing the analog-to-digital/programmable thermostat switchovers, but I have not been able to find the following info:

- how to find voltage of the installed unit (no user guide/info available)
- where to measure the existing voltage (with voltmeter in hand of course)

I know most homes are of the 24-volt variety, as are the recommended thermostats available at Lowes, HomeDepot, et cetera (circa $25 for a single program), but I'm not sure WHICH one to get that will be compatible with the existing rig (2001 Thor/Tahoe model 28DB 5th wheel).

I've attached a picture of the existing wires on the Duo-Therm manual/analog thermostat for some clarity as to what we're looking at--albeit it appeared on the original that the labeling was blurred (cell phone photos!!! ); thus labels from left-to-right are:

- +7.5
- Cool
- Fur
- Hi Fan
- Fan
- Gnd

Any input from those that have more experience than I is appreciated. Thank you all in advance for your time.

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Old 01-06-2011, 11:11 AM   #2
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Location: hanson ma
Posts: 210
hi i would like to do the same as you and will be very intersted to find out if there is a digital replacment for the duo-thurm dominic wall thurmos. as you said most house tstats use 24 volts and none that i know of have a high/low fan speed switch lee

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Old 01-06-2011, 11:18 AM   #3
a k
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Hunter Thermostat
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Old 01-07-2011, 01:09 AM   #4
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Thanks for the pointer to that good article "ak"!!! I haven't tried it yet, but it explains SOME of the questions I had, but there was no mention of the voltage measurement. It DOES map the DuoTherm analog contacts to the more conventionally used home application (RH, RC, etc).

For the clarity of directly to what I posted, below are the "mapped" labels that are on the Hunter device and how it maps to my earlier post with the picture.


+7.5/Red/(not used)
Fur White W
Hi Fan/Blue/? (article mentions separate switch?)

The article 'ak' mentions is a bit confusing throwing in the use of a separate switch, but I haven't tried it yet, so the jury is still out. There is a "jumper" wire that the new Hunter unit has and that might be the solution to the article's mention of a separate switch. Here's an excerpt of that article:

"Duo Therm OEM Wire Color Hunter stat terminal
(Original) used in trailer
Ground Black or green "RC"
Fan Orange or Tan "G"
Cool Yellow "Y"
Ground Black or Green "RH"
Furnace White "W"
High Fan Blue Thru SPST switch
to "G" (Tan)
Red +7.5 volts DC not used
Hunter thermostat Heating System Selector switch set to "HG"... "F/C" selector switch to "F" ... "

I'll try an install with the new Hunter unit I bought tonight (Jan 6th) in a day or so and report back
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Old 01-07-2011, 01:32 AM   #5
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This link is for Duo-Them thermostats in RV heating and AC setups.
All work from your 12v power system, with control units in AC's to other AC than to furnace.
This is the RV Duo-Therm thermostat.
The controls in AC's will need proper thermostat to control furnace.

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Old 01-07-2011, 09:10 PM   #6
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Thanks '007' !!! That is exactly what I needed for the specs!!!! I have a less-functional model of the Duo-Therm in the :"Analog Control System" found in section "B1c"--see attached picture. I bought my rig brand new in 2001 and never saw the manual you referenced. Thank you so much!

As it is I need a new thermostat whichever way I go as it needs to be set at 81 degrees to warm the unit up to 65; at that, it'll go on, heats for a while, goes off REAL briefly, then back on again--goes through that cycle MULTIPLE times before it can get to the desired heat level.

Same issue with A/C, but unit doesn't fire on-and-off, but the thermostat is still not shutting at the appropriate/set temperature.

Updates to my thread here to others that have been referenced herein and on the WWW:

1. Hunter Unit purchased, model #44155 (see attached)
2. Purchased at WalMart, Woodburn, Oregon for $27 in January 2011

So from an inflation standpoint, there's been a 50% increase in price of similar model mentioned in the earlier referenced link/article (in this thread was quoted as $19+).
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Old 01-09-2011, 03:41 PM   #7
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Okay. . . I've finished swapping out the Duo-Therm (By Dometic) in favor of the Hunter model #44155. I will wait to post any further info here so as to wait for a full 24 hours of cycle to share the "working" wiring and photos.

So far, so good however with a manual increase to the heat and auto-shtoff of the system at a programmed time.

More tomorrow (Monday, January 10, 2011)

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Old 01-13-2011, 12:58 PM   #8
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My understanding is that many thermostats work by scavenging 24 volts from the furnace circuit board to operate. In a 12 volt RV that will not work. You have to find a thermostat that uses batteries to operate the T stat and it opens and closes relays in the t stat on internal battery power, like a Hunter t stat. My gripe with the Hunter is that you have to add a switch to control fan speed. All that said, I have done this upgrade on all my 5ers and have been extremely pleased with the results. The hysteresis on the digital t stats is much, much smaller then an analog t stat keeping the coach at a more consistent temperature.
-Paul R. Haller-

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