RV Duo Therm thermostat to any digital conversion...problems. - Canadian TV, Computing and Home Theatre Forums
 
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post #1 of 6 (permalink) Old 2018-05-15, 07:56 PM Thread Starter
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Red face RV Duo Therm thermostat to any digital conversion...problems.

For those with any RV's be it a motor-home, 5th wheel or pod trailer, especially if it was made before 2005, you know the thermostats I'm talking about. Small little thing with a slider, hi/lo fan and heat/cool switch. That's it.

Well I have watched, read, thought I understood, about how to replace the "analog" to an electronic. I just have failed.

To make things worst, the colors I have aren't anything like any videos I have seen.

So here is my dilemma. For those who don't know, RV's don't have a C wire to supply 24Vac, at least mine doesn't so it needs to run on backup batteries, which is fine by me.

This is what my Duo Therm looks like. I have written the colors but don't go by the colors to try to match something.

RED - 7.5 (I thought it was 7.5 volts but I see no reading on a multi-meter)
Yellow - Cool
White - Furnace
Blue - Hi Fan
Brown - Fan
Green - Gnd


Now on my Focus Pro 5000 by Honeywell, which is the thermostat of choice, I thought, has the following pinout:

Rc - Power
R - (Rc+R joined by jumper)
Y - Compressor Contactor
C - 24vAC common
W- Heat relay
G - Fan relay

As you can see, there isn't much to compare, at least to me it doesn't look like it. Can anyone tell me what could go from which connector to which?

Right now, I have heat working but nothing else. I also can't change the speed of the AC fans unless I ground the Blue and The green together. This is driving me insane!!!!

Home Theatre: Yamaha HTR-6190, Klipsch Speakers, SANYO PLV-Z4, TOSHIBA HDDVD, LG BD555C, Cerwin Vega HTS12 Sub, VIP2300, XBox 360, HTPC.
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post #2 of 6 (permalink) Old 2018-05-16, 11:18 AM
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Don't know the details but it's possible that's a purely mechanical thermostat due to the furnace being thermopile operated. A thermopile is a small device that generates 0.75v of electricity from the furnace pilot light. Thermopiles are were once quite common in house furnaces but are now limited to niche markets such as fireplaces and stoves. A standard 24v electronic thermostat will not work. I've seen battery operated electronic thermostats that will work with low voltage furnaces, fireplaces and stoves. Waite was one company that made them. They would probably need to be sourced from a heating supply wholesaler or the manufacturer. eBay is another possibility.
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post #3 of 6 (permalink) Old 2018-05-17, 12:52 PM
 
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Blue-high fan, you won't find anything on a regular thermostat like that.

You have to see what it's function is.

When the system isn't 24v, any electronic stat used must be battery powered and use mechanical relays.

Even the regular mechanical stats have a heat anticipator resistor and only work on 24v systems. Have to get a stat without an anticipator for these systems.

Don't know much about rv furnaces, but if you give me the model number i can look it up and see what kind of controls it uses. It's not likely to be millivolt, especially considering the system has a/c.
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post #4 of 6 (permalink) Old 2018-05-17, 01:06 PM Thread Starter
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The part that bugs me is that there is no color code the same in all RV's to start with. In mine, behind the thermostat and right at the furnace, the colors changes 3 times!!!! How am I supposed to make tail and ends with that?

I understand I have to put a switch on the blue line for hi/lo fan. I just want to know why my AC doesn't kick in. Only the fans hi/lo.

So I guess no one has an RV on here and did an analog to digital thermostat conversion without having to add 24 volts?

Home Theatre: Yamaha HTR-6190, Klipsch Speakers, SANYO PLV-Z4, TOSHIBA HDDVD, LG BD555C, Cerwin Vega HTS12 Sub, VIP2300, XBox 360, HTPC.
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post #5 of 6 (permalink) Old 2018-05-17, 04:21 PM
 
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Seems no one does.

You have to see how the system operates, the low fan/high fan business.

Wire colours mean nothing, the installer selects and it's whatever is available.

Post the model number of the old thermostat, the furnace, the a/c and i can probably find the manuals, figure out how the equipment is controlled. For example, it may need high fan for a/c or the fan speeds for everything but continuous mode are controlled by a circuit board. (on residential stuff, there's a fan terminal G but with power to Y most new boards will bring on the cooling fan speed)
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post #6 of 6 (permalink) Old 2018-05-18, 07:33 PM Thread Starter
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Angry

I'll see what model my Duo Therm thermostat is. It is as basic as basic can be. Tons of people have succeeded. Not me. I must have the RV that was made either on a day after 3 day weekend or the day before 3 day weekend.

Home Theatre: Yamaha HTR-6190, Klipsch Speakers, SANYO PLV-Z4, TOSHIBA HDDVD, LG BD555C, Cerwin Vega HTS12 Sub, VIP2300, XBox 360, HTPC.
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