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AtomicNo13 · 07-09-2012, 06:42 AM

I'm looking to integrate my furnaces and roof AC into one digital thermostat.

I don't like having an individual thermostat for each.

What have you used?

HowieE · 07-09-2012, 07:47 AM

If your 91 Excella is the same as mine the stat for the AC is built into the unit. That connection has not only the stat wires in it but also the control wires for the fan and the AC on/off. The heater stat is a very simple mechanical switch that should never give you a problem.

Why attempt to change one of the few systems that Airstream may have gotten right?

AtomicNo13 · 07-09-2012, 08:22 AM

Not sure about yours, but regarding the A/C...

My A/C blower runs constantly. It never shuts off! Only the compressor cycles on and off. I called Dometic a long time ago and was told that AS specified their build this way!

If you use the t-stat wiring on the back of the control board, an outboard t-stat will allow the blower to be cycled along with the compressor.

The constant noise of the blower can be annoying, especially at night. Additionally, having the blower on all the time, just keeps the coach humid...

I think these systems are far from having gotten it right!

Even in the 90's, other manufacturers offered integrated HVAC thermostats.

Skater · 07-09-2012, 08:41 AM

Funny...I like having the blower on constantly. Having it cycle on and off wakes me up at night (I know this because the furnace does it).

I can think of two potential problems:
1. I assume the AC control board has to be designed with this in mind. If it isn't, you'll need an air conditioner that is.
2. If it is possible, how are you going to run the wires? Getting it through the shell will be hard.

AtomicNo13 · 07-09-2012, 09:14 AM

My Penguin has provisions to add an outboard t-stat, this way you get the cycling blower.

I already ran the wires from the A/C to the bedroom (where my furnace t-stat already is) it was simple, I just ran it down the hallway ceiling, then down into the closet then through the wall to the new location.

With a fiberglass snake, all is possible!

HowieE · 07-09-2012, 09:43 AM

Quote:

Originally Posted by AtomicNo13

The constant noise of the blower can be annoying, especially at night. Additionally, having the blower on all the time, just keeps the coach humid...

I have to ask the foundation for this statement. To the best of my knowledge a trailer AC has NO Outside Make Up Air. Yes to balance any AC system the blow should be on all the time. Some of the newer AC have redesigned the fan side to be quieter.

perryg114 · 07-10-2012, 02:00 PM

You can hook them both to the same thermostat but it is going to take some work. You will have to figure out which physical lines go to the AC and which go to the furnace. I don't know what the standard is for thermostats. I think they use to be 24 DC at one time but I am not sure. You would need relays to turn your units on and off. The voltage from the T-stat would operate the relays. I believe both the AC and older furnaces use a simple bimetal or mercury switch that operates the AC compressor directly and a relay in the furnance. You are going to need to know a little about circuits and relays etc. I am assuming that your AC has the build in T-stat and that the points in there turn the compressor on and off. I seem to remember points in those getting dirty when I lived in a trailer in college.

Perry

sandlapper · 07-10-2012, 03:55 PM

The PO of my '93 34' had installed a wall mount thermostat. It is on the frig wall, beside the furnace stat. Works great . Set it on the desired temp, it cyces the blower and comp just like one at home.

My son has a '90 34', & with the help of a HVAC buddy, we converted his the same way. It also works great. I fished the wire from the ac over to the wall, he hooked everything up. All I know is he used some relays, and did something up on the unit itself.

The only other thing I know is that it can be done, you just might need a good HVAC tech. My bud also has a trailer so he was happy to do it. His part only took about an hour.

I was content to leave the furnace stat as is. It is on the same wall.

Good luck, hope it works out for you. I sure do love it when the AC cuts off from time to time.

John