Dometic LCD Thermostat

[AG4SM]

We just got this trailer in October so have only used it a couple times. It has this Dometic thermostat which controls both AC and heat. I did not get a manual with it in the trailer packet, so I don't know much about it other than what I've read online, so I am hoping someone can shed some light on these quirks I'm seeing.


I read somewhere that when running the heat, to first go to the fan mode and turn the fan to auto to keep the AC fan from coming on when the furnace kicks on. That worked great.


This past weekend, we went camping and it was warm enough to run the AC for a while, so I turned it over to AC and set the temp to 70 or so (I wish this thing would show current amibient temperature). The AC came on, but sometime during the night, I woke up hearing the AC short cycling. The fan would kick on and run for 10 seconds or so and kick off. Then a few seconds later, it would kick back on again. (The fan mode was still set to Auto). I switched the thermostat over to Low fan mode and the AC seemed to cool fine the rest of the night. I was scared that the darn thing was trying to short cycle the compressor also, which will kill it eventually.


Lastly, this morning while the trailer is parked at my house plugged into shore power while cleaning it out, I walk outside and hear the roof AC running. It is 30 degrees outside. I could not tell if the compressor was running or not, but why would the AC even be running when the thermostat was set to cool with a temp setting of 70 degrees? (I had left it set to AC the other day to help dehumidify the inside since it had been raining on our trip). If anything, the furnace should have been running except the propane was not on AND the thermostat was in cool mode, not heat. Very strange behavior.

[270S]

The same thing happened to me when the temp dropped into the 30s for the first time last year. I think the thermostat shivers and turns on the AC by mistake - stupid S__T products in the RV world!

[Flybob]

Try initializing Thermostat.
Make sure the Single Zone LCD thermostat is in the Off condition.

• Press the “+” button and, while holding it, also press and hold
the On/Off Mode button for three seconds. LCD will show
― ― . Press the On/Off Mode button again to turn system off.

[D W]

Originally Posted by Flybob

Try initializing Thermostat.
Make sure the Single Zone LCD thermostat is in the Off condition.

• Press the “+” button and, while holding it, also press and hold
the On/Off Mode button for three seconds. LCD will show
― ― . Press the On/Off Mode button again to turn system off.

X2. And here's a manual for you:

[5picker]

While I don't have this particular model thermostat, I've read on several forums where the short cycling fan is a somewhat normal thing.

It seems the 'stat (or a sensor nearby) samples air to determine whether the unit needs to kick on/off. It is sampling air during this short fan cycle mode.

Every post I read, the OP complained they didn't like what it was doing even when told that is the way it works so it must be obnoxious. I've not read of a way to make it stop.

Just passing along what I've read...

[D W]

Originally Posted by 5picker

While I don't have this particular model thermostat, I've read on several forums where the short cycling fan is a somewhat normal thing.

It seems the 'stat (or a sensor nearby) samples air to determine whether the unit needs to kick on/off. It is sampling air during this short fan cycle mode.

Every post I read, the OP complained they didn't like what it was doing even when told that is the way it works so it must be obnoxious. I've not read of a way to make it stop.

Just passing along what I've read...

During my PDI, the tech talked me through "initialization" and I have never had any of these problems.

[Norcalace]

x2 on Initializing. Also you can read the ambient temp by selecting Off on the mode button then press the up or down arrow to display the temp.