Auto switching cool/heat thermostat?

Morich · 01-14-2020, 09:11 AM

Going to be changing the thermostat to digital and wondering how it works for other folks. I can see some value in auto switching from heat to cool but I can also see there might be some problems with RV use. I do not want programmable nor smartphone access as they are not useful for my RV time.
The question involves the allowable temperature swing between providing heat versus turning on the other. I understand there is a limit of four degrees swing and that would seem to leave it open to switching from one to the other too often as a RV temps are much more frequent than home use.
So how does it work for you folks? Do you find it switching too often? Like on a cool day that has required just a bit of heat, does sun shining on the thermostat cause it to switch to cooling?
Is the auto switch something that helps or does it just confuse the issue more than needed?

**ThomB** · 01-14-2020, 09:17 AM

I'll be interested in the answer. I've not tried to replace either of my thermostat's. My current solution is set one to cooling at a higher temp and the other to heating at the lower temp then hope that the temp difference between the front and back isn't such as they both kick on at the same time and they fight each outer.

Morich · 01-14-2020, 09:37 AM

In our situation, we have swapped the bigger RV for the short, to allow us more access to the nice parks, etc. that we prefer. That comes with some downside as things like the thermostat wind up much closer together and temps swing more as we do various things. Like taking a good hot shower or baking some biscuits and the thermostat is only 4-5 feet away?
Hate the thought that my hot shower would prompt the thermostat to switch on the AC!!
cost difference on the two thermostat is very little but I wonder if I'm just setting myself up for complications. Maybe there really is a reason for slow acting bimetal type thermostats in RV.

NeilV · 01-29-2020, 07:46 PM

What RV are we talking about?

My 2001 Adventurer came with an RV Comfort/Coleman Digital thermostat that controls both AC compressors however it does not automatically switch between heat and AC like the one in my home does. The auto-switching thermostat in the house does on days with a wide temperature swing sometimes provide AC during the day and heat at night however that is the whole point of having an auto-switching thermostat being able to set it and not worry about whether it will change from hot enough to need AC during the day and cold enough to need Heat in the late day to early morning.

Since you do not want humidity from a hot shower or cooking building up and damaging the coach you should always use the bathroom or kitchen vents while showering or cooking so a hot shower or cooking doesn't really present that problem of switching on the AC when you really want heat. You do have to use an RV as intended opening and turning on the vents to prevent humidity from damaging the coach when cooking or showering.

If you forget to open the vent and the heat and humidity from cooking or your steamy shower builds up to high enough levels to trigger the AC to automatically come on is it really a bad thing for the system to make up for that error and take care of things before you get a damp musty coach or have walls and windows with condensation dripping down them?

Morich · 01-29-2020, 08:25 PM

Quote:

Originally Posted by NeilV

What RV are we talking about?

My 2001 Adventurer came with an RV Comfort/Coleman Digital thermostat that controls both AC compressors however it does not automatically switch between heat and AC like the one in my home does. The auto-switching thermostat in the house does on days with a wide temperature swing sometimes provide AC during the day and heat at night however that is the whole point of having an auto-switching thermostat being able to set it and not worry about whether it will change from hot enough to need AC during the day and cold enough to need Heat in the late day to early morning.

Since you do not want humidity from a hot shower or cooking building up and damaging the coach you should always use the bathroom or kitchen vents while showering or cooking so a hot shower or cooking doesn't really present that problem of switching on the AC when you really want heat. You do have to use an RV as intended opening and turning on the vents to prevent humidity from damaging the coach when cooking or showering.

If you forget to open the vent and the heat and humidity from cooking or your steamy shower builds up to high enough levels to trigger the AC to automatically come on is it really a bad thing for the system to make up for that error and take care of things before you get a damp musty coach or have walls and windows with condensation dripping down them?

Oh yes! So busy thinking along one line and forgetting the details! You are right on the humidity part and we do try to fit the vents, etc. to clear it. Just not thinking about doing that when thinking about the auto switching. Thanks for pointing out that it will kind of take care of itself.
Meanwhile I had kind of moved on from the first thought and concern about the auto switching but just due to luck of the draw.
I found a guy who had redone his home system to get programmable and giving away the almost new non-programmable digital that are only a year or so old. Since I don't keep any reasonable schedule to program to in the RV, they are just right for what I want to do.
Thanks for setting my mind a bit closer to right!

rgvtexan · 01-30-2020, 10:49 AM

Check the operating voltage of the thermostat. Most residential stats are 24V AC.

Some use the backup battery for operation of the clock and program only, and not the control.

powercat_ras · 01-30-2020, 12:24 PM

What you need depends on:
- do you have AC unit with heat strip or AC with Heat Pump?
- do you have multiple AC units or mutiple Propane Furnaces?

You'll want a RV specific one that powers off the 12 volts DC that is fed to the thermostat, and switched thru to turn on the AC and Furnace. The typical RV specific ones have to be manually switched between Cooling and Heating.

If you just have one AC unit and one Propane Furnace then this appears to be the best value for that purpose at about $ 75 :

Coleman Airxcel

If you have a Heat Pump rather than just AC then this one won't do, you'll need a different one.

Morich · 01-30-2020, 06:58 PM

I've gotten past the auto cool heat switching and now am hung up on the wiring as my wiring is not the same colors nor labels on the new as the old. Some seem to match but several do not, so I'm still looking for info on which goes where but the idea is reasonably simple as I have a very simple coach.
Furnace is simple gas fired with no electric heat and the air is on the roof with no heat either but they do share the thermostat. I find lots of U-tube advise but they all seem to have two speed fans which I don't. Single speed on both heat and air.
With time to work the question, I will eventually go for just trying a few things as I have two stats which I got for free but then I also know that I might risk a few parts in the furnace or air and really don't want to get that shaky!
I think the main item for the stat is to get a milli-volt one which uses batteries for the operation and simply passes the signal through. That makes feeding it 12VDC rather than the regular house voltage of 24 VAC being okay as it doesn't involve any of the internal components except the relay passing either AC or DC. I see this much on the videos of folks doing the switch but many of them are going to programmable and I don't have any need for that when in the RV as we are not full time and on no schedule that we could set.

Morich · 01-31-2020, 09:08 AM

I often talk down about U-tube as a way to get info but there are times when they do the job and still is one that I liked for getting the main points on wiring a thermostat for my situation.

https://www.youtube.com/watch?v=fzH3vTZe3Qc

This person does a bit more actual showing and seems to understand better than many other vids I've watched on the subject.
One big point that can clear some confusion is that he does describe as well as show how the Honeywell operates on batteries rather than using 24VAC as many home units do it. He demonstrates that the thermostat only does the switching of the RV 12VDC but uses the onboard batteries to operate its internals. Put the batteries in and click the heat setting up and hear it click!