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AJMike · 03-01-2022, 09:28 AM

My RV (2020 Regency Ultra Brougham) uses a Dometic CT Thermostat to control both the AC and the propane furnace. While the thermostat does seem to do a decent job of regulating the temperature, both for AC and the propane furnace, it does not work like the manual says it should.

There are 3 fan settings - High, Low and Auto. According to the manual High and Low are supposed to set the fan so that it stays on all the time while the AC (and furnace) switch on and off, and Auto is supposed to set the fan so that it switches on and off with the AC or furnace, but Low is acting like Auto. That is, when set to Low the fan turns on and off with the AC.

That is a problem because the AC is not ducted and when set to High the fan makes a lot of noise, making for me it difficult to sleep at night. The Low fan setting is much quieter, but then the noise of the AC and fan switching on and off wakes me up. I assume that a Low speed fan would mask the compressor noise and make it easier for me to sleep if it stayed on all the time as it is supposed to.

The manual for the thermostat does not contain any wiring instructions so I don't know if it is a bad thermostat or if the connections to the device are wired incorrectly. There are 3 wires and as I remember the connections are 12v+, 12v- and comms, so I have a question.

It seems to me that, given only those 3 connections, if the device is wired improperly that it probably would not work. Is that correct? Or is it possible that this is a wiring problem rather than a device problem? Dometic has offered to send me a new thermostat (free. Who would have thought?) but I don't know if this is more likely to be a wiring or device issue. Perhaps someone with some experience with these thermostats can give me some help.

Old-Biscuit · 03-01-2022, 10:46 AM

Cool Mode:
Lo Fan....comes on when A/C first starts then fan runs continuously and compressor cycles on/off
Hi Fan....comes on when A/C first starts then fan runs continuously and compressor cycles on/off
Auto......comes on when A/C first starts.
In auto fan the compressor and fan cycle On and Off with the thermostat.
When the difference is:
>5º The fan operates on HIGH
<4º The fan operates on LOW

Heat Mode:
Lo Fan......runs continuously when furnace starts then furnace cycles on/off
Hi Fan......runs continuously when furnace starts then furnace cycles on/off
Auto....fan does not run when furnace runs
**Fan Mode of thermostat controls A/C Fan functions

If Fan Mode on thermostat is not controlling the A/C Fan functions then issue could be with the thermostat, incorrect 'phone cable' wiring, dip switches on A/C control module

I would take up the offer from Dometic for a new Thermostat and go from there.

*could be 'initialization' issue
Redo and see if it changes anything
Factor Default is Fan Auto
See pg 3-4
https://epi.dometic.com/externalasse...ef=-1379100643

AJMike · 03-01-2022, 11:20 AM

Quote:

Originally Posted by Old-Biscuit

When the difference is:
>5º The fan operates on HIGH
<4º The fan operates on LOW

I am curious about this part of your comment. Does it refer to the Auto setting? And only the Auto setting?

Quote:

Originally Posted by Old-Biscuit

*could be 'initialization' issue
Redo and see if it changes anything
Factor Default is Fan Auto
See pg 3-4
https://epi.dometic.com/externalasse...ef=-1379100643

I already reset using the initialization setting and it did not change anything.

Thanks for the manual link. I already have about 6 different versions of the manual that I got from various places on the internet, including from Dometic's website, but most of those refer to the bluetooth model and I don't have that. I don't know if the other information in those manuals is correct for the non-bluetooth model. When I spoke with Dometic they told me that the bluetooth model would not work to replace my model as it required a different controller.

As for the dip switch settings, I can get up on the roof and check, but I don't know what they should be so I have no way to compare what they are set to against what they should be.

Can you address my question about the wiring connections? Would the device work at all if the wires were not properly connected to the proper terminals? I would not think so, but then I am not knowledgeable about this sort of thing beyond the basic electrical concepts and theories. Spent too much time in Physics classes and not enough in Shop classes.

Old-Biscuit · 03-01-2022, 11:28 AM

In auto fan the compressor and fan cycle On and Off with the thermostat.
When the difference is:
>5º The fan operates on HIGH
<4º The fan operates on LOW

Dip Switch settings....need to check the A/C Model Installation Manual
Not thermostat manual

Wiring.......'phone cable' ---doubtful it is the issue
Lo fan and Auto wire connections inside the 'jack' could be wrong

Teamfoxy · 03-04-2022, 05:00 AM

To use the furnace, the fan must be set to "auto". It will not work with the fan set on high or low. Unless you have two furnaces, only the zone 1 thermostat should control it. There are also dip switches on the control board inside the AC shroud on the roof AC units that need to be set correctly.

A1RVTraveler · 03-04-2022, 06:19 AM

In your situation (CT Version) you have three wires going from the thermostat to the control box in the ceiling. Ground, 12volt plus, and communication. There will not be a phone cable. You DON'T have a wiring problem. There are no Dip Switches for you to check.

I have never seen a system that did not run the fan in LOW as you described.

Take Old-Biscuit's advice and change the thermostat. If this does not fix your issue, change the control box. Ask Dometic to send you the complete kit which included the control box and thermostat. Never hurts to ask.

bduemig · 03-04-2022, 06:39 AM

I have never had any luck with Dometic thermostats. I offered an Easy touch thermostat that also has Wi-Fi so I can monitor temps while away from the motorhome.

https://www.microair.net/products/ea...-rv-thermostat

AJMike · 03-05-2022, 06:16 AM

Quote:

Originally Posted by Teamfoxy

To use the furnace, the fan must be set to "auto". It will not work with the fan set on high or low.

Well, yes, it does.

In fact the propane furnace runs with the thermostat set to either High or Low. Since I don't keep it on Auto I can not say if the propane furnace also runs on Auto.

Quote:

Originally Posted by Teamfoxy

Unless you have two furnaces, only the zone 1 thermostat should control it. There are also dip switches on the control board inside the AC shroud on the roof AC units that need to be set correctly.

The CT thermostat is a single zone thermostat and our RV has a single propane furnace along with a single heat strip in the A/C. Well, to be honest, I have never run the heat strip in the A/C so I am assuming it is there because the thermostat has a setting for it.

AJMike · 03-05-2022, 06:23 AM

Quote:

Originally Posted by A1RVTraveler

I have never seen a system that did not run the fan in LOW as you described.

I am sorry, but your meaning is not clear to me.

Are you saying that all of the systems you have seen run like I described our system as running? That is, on Low the fan switches on and off with the A/C.

Or are you saying that all of the systems you have seen run like I said the manuals says it should run? That is, on Low the fan stays on all the time.

Quote:

Originally Posted by A1RVTraveler

Take Old-Biscuit's advice and change the thermostat. If this does not fix your issue, change the control box. Ask Dometic to send you the complete kit which included the control box and thermostat. Never hurts to ask.

I have already asked them to send me a replacement, and I will test it when it arrives. I should also ask where the control box you mention lives. In the roof A/C? Or somewhere in the wall wiring?

A1RVTraveler · 03-05-2022, 07:30 PM

Sorry for the confusion. You do have an issue with your RV. The fan should always be on when in the Low or High position.

The fan cycles off when you are in Auto and the proper temperature has been reached.

The control box is gray in color and usually located in the airconditioner ceiling assembly. You should be able to see it if you have a removable plastic grill for the AC filter in the ceiling.

Teamfoxy · 03-06-2022, 04:39 AM

In our 2005 Itaska and our 2011 Mirada, the furnace blower would only operate when the fan was set to auto. Only the front thermostat would operate it. There were no heat pumps. Our current Canyon Star is different in that both front and rear AC's (with heat pumps) are controled by a single unit that also controls the furnace. During our PDI, the furnace did not even show up on the control which resulted in the AC tech comming out. The problem was reported to be a dip switch setting in the forward AC unit. The switches were fairly well hidden and he had to take a picture with his phone and then enlarge the photo to see the positions and settings. He showed me the picture.
Given the different controls, furnaces, and AC units over the years, operating them does vary from one coach to another. We all offer advise based on what we have experienced in the past. Sometimes it helps and sometimes it doesn't.

AJMike · 03-06-2022, 08:01 AM

Quote:

Originally Posted by Teamfoxy

We all offer advise based on what we have experienced in the past.

Of course. Unless we are certified techs or were involved in the development of the item in question our experience is all we have to base our comments on, and that is what people who post questions, like myself, are asking for. What have others seen or done in the past.

As for me, I am grateful for any information even though I know if may or may not apply to my particular case, so I am grateful for your posts.