Honeywell RTH5100B Thermostat

[2000_Kiwi]

The thermostat upgrade is a very common upgrade and lots of information is available on this forum. I wanted to add the specific model I used for others that may be searching.

Honeywell RTH5100B 1025 Deluxe Manual Thermostat

I picked this specific model because it had the "automatic" switching between heat and a/c. In Spring and Fall the day and night temperatures can vary significantly.

This model is also battery operated so there is no need to power the unit separately; just make sure you keep extra batteries on hand. My next mod may be to take a variable voltage regulator (LM317) and connect it to the 7.5v supply provided for the Duo Therm and power my Honeywell.... But this is not a priority.

Please note that your wire colors may vary. With this configuration you will lose the HI/LO fan option. This will give high fan only.

There are other posts in this forum that will show you how to add a separate switch to maintain the dual fan settings.

The original analog Duo-Therm by Dometic


Duo-Therm Wiring


Honeywell Wiring


Honeywell Installed


Wiring Diagraim


It is important to note that you will need to follow the setup guide to select the correct parameters. For example: the auto feature where it switches between heat and cooling is disabled by default.

[Chris_Bryant]

DuoTherm (Dometic) uses two relays for fan control on these boards- the brown fan lead switches power to the fan- this must be connected or the fan will not run. The blue high fan relay simply toggles between high and low fan, so you hook the brown wire to the new fan circuit, the blue wire will connect to this circuit via a simple switch to combine the two.

[SoundGuy]

Fisherguy wrote:
If a person wanted the seperate switch for high and low he would wire the switch to that lug as common on the switch?

Yes. Also make sure the switch has a centre off position and one can then start the A/C using a 2K genset and have the initial load the genset has to deal with reduced by the amount of load the fan would otherwise present ... once the compressor ramps up to speed, simply turn the A/C fan on. Works like a charm.

That seems pricey for a non prgrammable thermostat isn't it?

~ $32 US or $50 Cdn is "pricey" for a thermostat that's such an improvement over any stock bi-metal thermo? :h

[Fisherguy]

JUst wondering, you have the 2 'fan' wires both going to the same lug on the thermostat? If you only wantedthe high spped to work couldn't ou just vconnect the 'hi speed' wire?

If a person wanted the seperate switch for high and low he would wire the switch to that lug as common on the switch?

That seems pricey for a non prgrammable thermostat isn't it?

[2000_Kiwi]

Dakota98 wrote:
Installed mine last Spring.

By far, an improvement over the old one!!!

Nice info/control center!

[Dakota98]

Installed mine last Spring.

By far, an improvement over the old one!!!