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Thermostat Control Positions

Posted: Fri Oct 30, 2020 2:07 pm
by Safaritoonces
I have the Duo Therm AC & Hurricane heater control thermostat. I have replaced it with two LCD panels, one for each function heating and cooling. I used two because of technical reasons and they were ones I had on hand. Eventally they will be changed for a single unit now that I have them working correctly.

Here is my question. How does the original system work? There is a High/Low switch and a separate switch automatic position for the fans. If the switch is on low or high and automatic do the fans come on and off automatically until the temperature is correct? If on low for example does the fans run continously?

In the bedroom and shower area there are switches that say Heater On and Off. I don't understand this. What purpose does this serve because there is an on/off position on the thermo stat?[
Duo Therm Thermostat
Duo Therm Thermostat
20201029_175316.jpg (1.95 MiB) Viewed 10423 times

Re: Thermostat Control Positions

Posted: Sat Oct 31, 2020 8:42 am
by Jeffjordan1972
Robert,
The hi lo is fan speed on the AC unit. Auto means the fan only runs when the Thermostat calls for the ac compressor to kick in. On means the fan runs all the time.

Regarding the heater on off switches for your hurricane, I believe they turn the radiator/heat exchanger fans on and off in those zones. The hurricane gets “told” when to fire by the Dometic thermostat calling for heat and it will also cause the fans in the radiators/heat exchanger to come on but if you do not have those switches turned on they will not blow air across the heat exchanger/radiator. This could be useful if you wanted to, for example, use the hurricane to heat your domestic hot water without heating up the cabin further. Or if you want the hurricane to get up to temperature before you start moving air around so you’ll feel less chilly.

Re: Thermostat Control Positions

Posted: Sat Oct 31, 2020 12:59 pm
by Safaritoonces
This now makes sense. The auto switch applies to the AC only. The low and high is for the AC fan speed only, with the heater speed control for the heater fans being the two separate controls.

This will make it easier to wire the controllers.

It was a slightly bizarre way of doing things, but I think they were trying to use the same temperature sense circuit and controller to regulate two separate devices.

I will post the project when it is done. Thank you for the explaination.

Re: Thermostat Control Positions

Posted: Tue Nov 03, 2020 8:11 pm
by Safaritoonces
In the bedroom and shower area there is a high/off/low switch I understand now controls the heater fans in these two areas. In the control center cabinet in the kitchen next to the fridge, that has the tank levels, there is an heat on/off switch below the hurricane on/off switch. Is this the fan speed for the salon and kitchen areas? I have the controls apart right now so I can't test them.

Re: Thermostat Control Positions

Posted: Mon May 17, 2021 2:38 pm
by chuckster
Safaritoonces wrote: Fri Oct 30, 2020 2:07 pm I have the Duo Therm AC & Hurricane heater control thermostat. I have replaced it with two LCD panels, one for each function heating and cooling. I used two because of technical reasons and they were ones I had on hand. Eventally they will be changed for a single unit now that I have them working correctly.

Here is my question. How does the original system work? There is a High/Low switch and a separate switch automatic position for the fans. If the switch is on low or high and automatic do the fans come on and off automatically until the temperature is correct? If on low for example does the fans run continously?

In the bedroom and shower area there are switches that say Heater On and Off. I don't understand this. What purpose does this serve because there is an on/off position on the thermo stat?[20201029_175316.jpg
I have this same Dometic thermostat in both the front room and bedroom in my ‘01 Zanzibar. I am wanting to replace them both with an inexpensive Honeywell or other digital thermostat so I am not guessing at what the temperature is set at. Does anyone have a recommendation for a simple digital thermostat that will work fine? I don’t want or need any fancy Bluetooth or WiFi thermostat.

Re: Thermostat Control Positions

Posted: Sun Aug 21, 2022 7:22 pm
by chuckster
So I went to Lowes and picked up a cheap Honeywell thermostat with an LCD display. It has a switch inside the thermostat to let you select gas/oil or electric/heat pump. I think it should be set up for the latter. Not sure if this will work in my ‘01 Zanzibar or if I should even attempt it. I am posting some pics of the Dometic thermo, the Honeywell and relevant pages of the manual. Not sure what the +7.5v wire does or goes to.

I have the same Dometic thermostat in the bedroom and no clue if the heat setting in there really does anything. It may, I just don’t recall.

Any input anyone?

Re: Thermostat Control Positions

Posted: Fri Apr 28, 2023 5:15 pm
by chuckster
I never did try this Honeywell digital thermostat to replace the Dometic thermostat in the living room and bedroom. I never got any feedback or direction on this so If you are willing to review the thread and respond, I shall be grateful. I assume that the Dometic thermostat in the back only controls the A/C in the bedroom and not the heater but I have been wrong twice in my long life already. :lol:

Re: Thermostat Control Positions

Posted: Fri Apr 28, 2023 9:01 pm
by TDJohn
On my coach, only the front thermostat performs the heating and cooling functions. The rear one just does the cooling. That said, some coaches had dual furnaces, in that case, I would imagine that the rear thermostat would control heat for the second furnace. Also, coaches with hydronic heating, used both thermostats to control the fans in the heating registers in the front and rear of the coach. If you don't have hydronic heating, and just have one furnace, then your rear thermostat just controls the cooling side of the bedroom. I would suggest to know and label all the thermostat wiring, to know what controls the a/c, the a/c fan, which has high and low function, and in the case of the front thermostat, the heat/furnace function. That is a lot of wires that can get mixed up if not traced and labeled. I vaguely recall someone mentioning that some of the new thermostats have different function that are in similar locations of the old OEM thermostat. So one can easily get things mixed up. If the old thermostat is labeled as to what connector does what function, and you have not removed the wires from the thermostat yet, then it would be real easy to label all the wires, w/o needing to trace them.

As for your other question. I don't know if your Honeywell thermostat is for heat only or heat and a/c function. If it is for heat only, then I don't think it will work. If it is both, I think you still will have a possible or likely issue of your a/c fan going on, when the thermostat kicks on the furnace. The only fan you have is the a/c fan, the furnace fan works automatically, so you will likely have a compatibility issue.
The brown wire likely is the wire that allows you to turn on the fan only, with out the a/c or thermostat function. It will stay on until you turn it off. You will see that option on your OEM thermostat...

BTW,are you having issues with the OEM thermostats???

If not, may I kindly suggest, that if it ain't broke, don't fix it. ;)

Re: Thermostat Control Positions

Posted: Sun Apr 30, 2023 7:49 am
by chuckster
Hi John,

No issues with the old analog Dometic thermostats other than the psychological assurance that we can know that if we want to feel 70 degrees inside the coach that we can set 70 degrees on the digital thermostat. I am thinking that perhaps it would be best to leave the old ones in place and just put a digital thermometer next to it and “not fix it if it ain’t broke”. :D

Re: Thermostat Control Positions

Posted: Sun Apr 30, 2023 8:05 am
by chuckster
Hi John,

No issues with the old analog Dometic thermostats other than the psychological assurance that we can know that if we want to feel 70 degrees inside the coach that we can set 70 degrees on the digital thermostat. I am thinking that perhaps it would be best to leave the old ones in place and just put a digital thermometer next to it and “not fix it if it ain’t broke”. :D

I do not have a dual furnace nor a hydronic heater.