Hello Barth Friends,
My roof-top air conditioner is the Dometic Duo-Therm 600 Series Penguin. It has a "four button Comfort Control" duo-therm thermostat located in the coach. It operates the furnace and the air conditioner. However, the thermostat has a very large degree of slop or hysteresis. When set for a particular heating temperature at night, the temperature drops an excessive amount before it comes on. Once on, the temperature rises too much before it goes off. I have not been able to find a brochure/manual for the thermostat. Is there any adjustment for this problem within the thermostat?
Does anyone have the thermostat manual?
Any suggestions ... that is, besides buying more blankets?
best regards from,
Allan of Solvang

Hello Allan
Not sure of your model, is there a heat anticipator on the thermostat?
Hope I may of being some help
Dalton

Hi Dalton,
I am not familiar with a heat anticipator. How do I determine if the thermostat has that feature?
Thanks,
Allan of Solvang

Remove the cover. There should be a screw or a strip with a movable slider. Usually, the slider should be lowered to compress the temps between cut-in and cut-out. The screw should have temp spread markings on it's dial; usually CCW compresses the anticipation.

Hi Rusty,
No such luck. Inside, the Duo-Therm thermostat has resistors, transistors, a few ICs, capacitors, diodes, etc. but no mechanical adjustments. Looks like a telephone type connector brings the wires inside. Nothing adjustable that I can see.
Any ideas?
Allan of Solvang

I just replaced the original A/C in mine with a Duo-Therm with the wall t'stat, so I took a look inside mine - same deal; I pulled the PCB to see it there were an adjustment on the back - nope.

A new t'stat seems to be in order - I don't think it'll run over $100 - that said, there may be an anticipator in the roof unit - the furnace relay circuit on mine is 7.5VDC, so there's something electronical up there. Duo-Therm's manuals pretty much suck, so a dealer may find it a mystery.

(I also left the original wall t'stat intact, because I can run the heat strip when it's cold, with the furnace to kick in if the strip isn't enough to maintain temp.)

BTW, it helps when members post the year and model of the coach; that gives us an idea what we're dealing with

Hi Rusty,
Thanks for your help! FYI: my Barth is a 1996 22' short Regency with the Chev. 454 gas engine. Perhaps the very last short Regency style built. If you find a suitable replacement stat, please let me know. I would be uncertain how to select a replacement because it operates both the air conditioner with heater strip and the propane furnace. I only have the installation booklet on the air conditioner, and it does mention a heater strip, but I have never noticed it working. How would I determine if the heater is actually functional in the air conditioner? Do you know of any replacement stats that would be more friendly.
best regards from,
Allan of Solvang

there should be a slot on the a.c selector switch that reads.."pre wired for optional heat". It will take a couple of minutes to warm up the element but if you do have a burner on that unit, you should feel heat coming off it in the two minutes.

quote:

Originally posted by Allan:
Perhaps the very last short Regency style built.

Don't you mean Regal??? BTW: Have you contributed your data tag info to our cause yet?

Also, to make it easier for everyone, I've given you a signature profile that has the following...

Best regards from,
Allan of Solvang

1996 22' short Regal with the Chev. 454 gas engine

If you send me a picture, or a link to a picture, I will include it in your profile.

Hi Bill,
Yes you are correct, it is a Regal. We purchased it new and are original owners. We had previous owned a 28' Barth which we traded in on the shorer unit. My purchase notes for this coach say "with Regency style of appointments." Please remind me of the difference between Regal and Regency?? I will work on the data tag effort.
Hi Kris & Tina Jones,
My only control for the air conditioner is the four button thermostat. Where is the "slot on the a.c selector switch that reads.."pre wired for optional heat" which you mention?
Thanks to all,

"Prewired for optional heat" means your roof air unit is prewired for a heat strip, should you choose to install one - it's a simple D-I-Y operation.

The new Duo-Therm electronic thermostat is probably a simple replacement for the wall one - with one caveat: It has to have chassis 12VDC supplied to the roof air - and yours likely does since it also operates the furnace.

There are connections for seven wires in the new thermostat (what appears to be telephone wire is actually thermostat wire - available at any home improvement center - but you shouldn't need any). Each is labelled clearly: (in no particular order) GND, 12VDC, Furnace, fan, heat strip, aux, and A/C. The new t'stat has a slider for temp setting and slide switches instead of buttons for selection. It's here, the top photo (Analog Control Center).

Hi Rusty,
A new thermostat seems like a good idea as it has the capability of using the heat strip instead of the overly powerful (for out here in California) propane furnace. And, it may have less slop or hysteresis which is my original complaint.
My next problem will be figuring out which wires are which because the old thermostat has all wires in what looks like an unmarked telephone type connector.
Do you have a schematic or manual for my old four-button Dometic Duo-therm thermostat? I can spot the 12VDC connection with a voltmeter, and most likely can identify the ground wire with an ohmmeter. Do you suppose that I can assume that "Furnace, fan, heat strip, and A/C" are all low voltage feeds out to relays? If so, I can arbitrarily connect and see what starts up! But a wiring diagram for the old thermostat would sure help.
Again, many thanks!

I think you can assume all the outputs are to relays. IIRC, BTW the 7th connection is for one of the fan speeds, not "aux".

My old unit had the control panel on the shroud; when I got the new unit and replaced its original shroud, I taped the t'stat to the shroud, then ran the wires and installed it on the wall.

So my old thermostat connected to everything with a ribbon cable.

Anyway, you should also be able to identify the wires with a voltmeter - see what terminal energizes with the switches in different positions.

quote:

A new thermostat seems like a good idea as it has the capability of using the heat strip instead of the overly powerful (for out here in California) propane furnace. And, it may have less slop or hysteresis which is my original complaint.

That's why I left the furnace t'stat in - it has adjustable anticipation, and I finally got it settled out to where it doesn't go from ice to fire...

Hi Rusty,
Oh, of course! I would just see which wires are hot when each function is on to identify the leads.

As I understand it, you left two thermostats in place. I guess that was because the new one, with a switch for heater strip, does not have an adjustment for heat anticipation. Is there not a thermostat that does everything? What about using a household thermostat?

Household thermostats run on 24VAC, unfortunately.

I kept the furnace thermostat so I can heat with the heat strip, with the furnace to kick in if the heat strip can't supply enough. One thermostat can't do that...

The factory-set anticipation on the new thermostat is a pretty narrow range, so it works well.

My adventure with the new A/C is here.