Thermostat

One thing to watch out for. When I installed it, the heater worked just fine, but the A/C seemed to work intermittently. It would work, then I would try it again, and it wouldn't. Was really puzzling. After tearing it apart and puzzling over it for hours, I decided to read the instructions :) Turns out that it (at least mine) has some sort of re-start protection that won't start the A/C unless it has been off for 5 mins.

Another interesting point. These thermostats normally requires +24V for power, which the house supplies, but we don't have on our RVs. This install will be running completely on the AA battery inside the unit, so you'll have to replace the battery on occasion. Seems to last a year for me. The supply connection is left unconnected.

The ground wire from your RV doesn't go to 'common' like you think it should (in fact it's left unconnected).. The ground wire goes to the RH and RC (heater/cooler power) connections since our units (at least mine) trigger on ground instead of the normal +24V. Backwards, but it works.

Double post

Although I prefer digital, as I recall there was a hysteresis control on many/most of the old mechanical thermostats. It was called an "anticipator" I believe and the ones I remember were a sliding metal arm that moved on a wire coil wound on a flat piece of insulating material. (A potentiometer in my world.)

Thanks everyone. Lots of good info here.

That was my first mod.. The old Dometic unit had a 6 degree swing before kicking in. The new one is about 1 degree between off and on.

This was the tutorial I used:

http://www.modmyrv.com/2012/01/03/mod-100-honeywell-digital-thermostat

My install:

Yes, get a new electronic stat and it will keep the "swing" or hysteresis much tighter.
The best but most expensive stats are those that are Energy star rated and use a microprocessor. I had to use one of those because our furnace is too big for the trailer and had a terrible problem with overshooting the temps.
An ES rated stat takes into account the cool down period of the furnace after it shuts off. Ours keeps the temp dead on now.
The famous Hunter stat worked ok but let the temp go over by 1~2 degrees.

No, the MECHANICAL tstat has the same ranges. So, getting a new one will not improve it much. A NEW tstat may function better as the spring and points are not as pitted and worn. Doug

Replacing analog thermostat using a digital was one of the best improvements I made to the motorhome. Below are some links that should be helpful to you.

Click here.