Dometic Duo-Therm 3105058 replacement

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Stahlmaster

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Aug 24, 2014
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The original thermostat is a Dometic Duo-therm #3105058.  I have a Hydro Flame forced air furnace and a 579 series BRISK AIR 590 Series QUICK COOL Roof top air conditioner. It worked fine for about a year.  This weekend while using the heat, I noticed a burning smell near the thermostat and found the anticipator had burned out.
I have two questions:
Can I solder a jumper around the burned out anticipator and bypass it?
What type of replacement would work?
It is a bi-metal type with the following 6 wire markings:
RC, G, Y, H, W, Rh

Thanks
 

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Gary RV_Wizard

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The anticipator is just a small heater which basically causes the t-stat to shut off the furnace burner a little bit early. Otherwise a bi-metallic type t-stat, which is slow to react to temperature change, actually overruns the set temperature. I would think the t-stat would still work if the anticipator resistor burns out (open circuit), but you might need to set the temp a degree lower to compensate.

Jumpering across the anticipator resistor probably won't work because there is no resistance at all, i.e. a direct short. Likely to burn out something else. I think you need at least some small resistor there.

Digital thermostats generally don't have anticipators - they react quickly enough that they aren't needed.
 

Gary RV_Wizard

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So does the thermostat still start/stop the furnace & a/c? Without the anticipator working? If not, it must be in series with something else in the t-stat.  You could solder most any small resistor in there to provide a circuit that does not look like a short, but not sure of the effect of the voltage drop on whatever else is in that circuit.
 

Stahlmaster

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Aug 24, 2014
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The heat was running and just stopped.  No blower, no nothing.  We do not use the A/C do to being off the grid and the generator we have is too small to run it. 

What I did was move the anticipator needle to a spot off of the burnt spot and it now seems to work on the bench test.

I'm not concerned with it being off a degree or two or 5.  Heat is heat to me.

I'll pop it in when we go up next and see how (if) it works.

With that being said, if I do need to replace the thermostat, what would work?

D
 

Gbine

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Oct 4, 2021
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Pennsylvania
My Thermostat also burned up and can anyone tell me if something in particular caused that. My RV furnace is a 8535 III and I don't have a battery on the trailer and would this have anything to do with this problem, thank you
 

NY_Dutch

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Nov 22, 2010
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Where our wheels take us!
I replaced the Hydro-flame 8525 and the 8535 analog thermostats in our motorhome with Honeywell digital thermostats. I used 7-day programmable stats, but there are non-programmable models as well. These stats normally get their power from a home furnace system, but the backup batteries last about a year in constant use. This is the model I used:

 

JayArr

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Jun 13, 2020
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Mission British Columbia Canada
Dutch has the right idea. Grab a Honeywell that uses a battery, mine are TH6220D1002, but you don't necessarily need one this fancy or expensive.

RC, G, Y, H, W, Rh looks familiar, here's what I know

Rc - 24V from air conditioner
G - Fan Relay
Y - Compessor contactor (AC)
H - ??
W - Heat Relay
Rh - Likely 24V from heater

Keep in mind that the thermostat was built for dozens of configurations so you may not use all of the terminals. Make good notes of which color wires go to each terminal before you undo anything.

The new Honeywell thermostat has all those contacts except H.
 

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