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Old 11-25-2007, 12:33 AM   #1
BigBoy2U
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Two thermostats one for AC, one furnace, has it been done?

OK this is a tad long but…just want to run this by you guys. What I am thinking of doing. So I am looking to see if anyone else has done this.

I just bought a used 05 36CK3 everything worked when I left the lot (figures) but we recently have had some cold (25 degree) weather in Seattle. I haven’t been able to move into the unit just yet. But the other day the furnace worked fine, it worked fine the day I picked it up. It was a repo so I knew anything that went wrong I was going to fix. The dealer would fix anything that didn’t work at time of inspection. So yes I did steal it for $40,500 and its in great shape just no furniture and need a good cleaning!

So I go to fire up the furnace one night since the unit is not winterized and nothing. I play around with the 5 button climate system, go online and get the instructions and still no go. Now I mean no fan, no cycling dead. (Ok this is where I know about propane levels, etc. But this is a NO power, no fan, no cycle, no try to start…nada, zip nothing.) Checked the fuses all OK. So off to read more than I ever wanted to know about the Duo-Therm Climate Control 5 button system. My system is set with 2 zones for AC and one zone for furnace. No heat strips and no heat pump. I tried the power down, switch the thermostat on and off, did the reset many times and still get FF. So I know its reading the CPU at the rear AC.

I am about to probe down to the furnace when I tug on the wires and sparks. I look and the wires are chafed where they leave the side of the furnace and the “On-Off” switch for the furnace is loose hanging there not attached to anything. The next day I pull the cover off the furnace to find (1. the trim ring is not even siliconed or sealed in any manor to the body, 2. the screws are all mismatched and half are lose and stripped. Now it doesn’t look like this has ever been out since the paint lines match up.) I just can’t believe DT didn’t even seal the plastic trim piece. So I also notice the plywood they filled between the fiberglass and the frame was wet from water running down the side of the exterior and then into the opening that was not sealed. (Anyone else have this problem?) You should all check your furnace trim ring and see if it’s sealed to the body. At least caulk it in place if its not.

Ok so I look at the wires along with all the mouse droppings and realize what happened. Mr. Mouse was living in the furnace and stripped half the wires. So I cut, replace and heat shrink tube the bad wires. Reposition the on-off switch and still furnace wont fire off. VOM the power, power ok, ground is good so next jump the thermostat wires and it fires off (well ok it was out of the unit but the blower motor run until it timed out.)

I have pretty much at this point come to two conclusions, 1. The thermostat is bad or 2. The control module up in the rear AC unit is bad for the furnace output and got fried with the wires shorted to ground. I am able to get the fans to run on all 3 speeds + auto on both zones (cant get the AC to kick on since its still in the 30-40’s here). So I have to guess that the module will work the AC (fingers crossed). Now I admit I have not taken the roof AC unit cover off and checked the wires. Could be no 12V at one of the furnace wires or a bad connection also. But it got me thinking...about doing this instead...

Ok so here is what I want to do: Install a separate thermostat for the furnace. At least I can get one that is programmable to turn down the heat and back up again a 7 day 4 program thermostat for $29 at Lowes. (I did the Hunter replacement on my Avion and this is a simple two wire compared to that install…lol)

Anyone see any reason why not to do this? I don’t see it being that much different than having to switch the “modes” on the 5 button to furnace. Just need to make sure the old 5 button AC is not set to run when the heat is on and make sure the furnace is off to run the AC in the summer. To me is really makes it a lot easier to have a complete system this way. Set AC to not come on until 77+/- and never set the heat above 73+/-. Two separate systems that can work as one. Set it and forget it and just leave them both on as programmed.

At some point I will get on the roof and set the dipswitches to remove the furnace from the 5-button program. So it won’t confuse anyone else and just label the thermostats properly.

OK fire away!
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Old 11-25-2007, 09:37 AM   #2
Motor31
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OK You have got a bit of diagnostics already done, great job on finding the issue with mice.

First off the furnace (propane) runs off of the thermostat in what is shown as zone 1 on the thermostat. Since you have dual AC units (I think that's what you indicated) the bedroom runs off of zone 2 and does not have the furnace on it.

Your rig MAY have one or two AC / heat pump units. They are not the furnace settings. The furnace will be labeled (in zone 1) as furnace and the heat pump will be labeled heat. The heat pump settings do show up first in line after cool on my thermostat (also an 05) then you click again to furnace. The thermostat temperature settings are the same for heat pump and furnace.

If you have a heat pump, changing the dip switches will change the heat pump but not the furnace. The furnace is a separate item only controlled by the thermostat and not the dip settings on the AC. If you do not have a heat pump again changing dip switches on the AC won't change the furnace situation.

If the furnace will run the blower but not light, you might want to check propane level and the regulator as well. See if the igniter is clicking. If the gas supply tube is blocked by wasp or other critter nest you may smell propane but not get enough to light the burner before it times out.

There have been folks who swapped out the thermostat in their rigs. You might want to try a search on this section of the bbs to find the threads. It was some time ago it was talked about.

Hope this helped some.
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Old 11-25-2007, 12:55 PM   #3
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Thanks for the reply, I am not intending to be rude...but this is just the road I didnt want to go down. As I stated the "furnace" wont even run the blower (meaning we can skip any other diagnostics since I verified the 12v power supply, ground and jumped the thermostat and it ran). This MS does not have heat strips or heat pump. The dipswitches do control the ability to add or subtract the zone 1 furnace from being shown on the thermostat control head (the wall unit) along with a whole host of other options such as heat strips etc. I have all the wiring diagrams, instalation instructions for the Duo-Therm Climate Control (those are all available on the duo-therm web site)

My real question is....why spend the money buying a new Duo-Therm control module or thermostat or both if you can just add another thermostat for the furnace only and gain better control like 7 day programming? Has any one else done it?
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Old 11-25-2007, 10:15 PM   #4
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Re: Two thermostats one for AC, one furnace, has it been don

Quote:
Originally Posted by BigBoy2U
I am able to get the fans to run on all 3 speeds + auto on both zones (cant get the AC to kick on since its still in the 30-40’s here). So I have to guess that the module will work the AC (fingers crossed).
Seems you should confirm the A/C function of the 5 button first. Otherwise you might be buying a new 5 button after installation of the 7 day furnace thermostat.

If the 5 button is OK for A/C, the programmable thermostat would be the way to go. I think it would need to be mounted on an interior wall (not behind the entry closet door) to detect temperature accurately.
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Old 11-26-2007, 12:33 AM   #5
BigBoy2U
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I think I am going to be stuck unit it warm up to run the AC....just hoping that the AC works OK from the module. I know it powers the fans in both zones so my best guess is that the circuit that controls the furnace went bad in the module from being shorted out. Worst case is this...I end up having to buy the whole Duo-Therm module and/or the 5 button wall unit next summer and I also have a new 7 day programble thermostat for the furnace only. I dont really see there being a negative to having the furnace on a seperate thermostat since its not backing up heat strips or a heat pump. If I had either of those I think it would have to be tied into the same controller to keep the AC from freezing up.

I know in some other posts people have indicated they wished the Duo-Therm 5 button was programable for heat in the morning and to turn down at night on its own. You would think that for the cost of this unit to add some simple energy saving programs would have been easy.

I am pretty convinced at this point to complete this tomorrow with a new thermostat and wait and see if the AC works when it warms up. Again worst case I need a new Duo-Therm module to make the AC work.
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Old 11-26-2007, 12:39 AM   #6
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Oh also it looks like the wall that the thermostat, CO detector and (my mind is blank at what the third item is next to hand rail) but that is an open chase to the electrical area as far as I can tell. So my plan is to mount the add on thermostat above the Duo-Therm.
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Old 11-26-2007, 01:18 PM   #7
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just a note to anyone following this thread; over on the yahoo groups I ran across a post that got into the thermostat issue. Since 03 or the use of the 5 button thermostat, the dealers and factory have been addressing the "no run furnace" by adding an Atwood thermostat next to the Duo-Therm and taking the furnace off the Duo-Therm dipswitch so you end up with two thermostats. I guess there is a problem with the control unit failing and this how they chose to address it.
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Old 11-26-2007, 02:39 PM   #8
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Bigboy2u: Yep, the cavity you're talking about is indeed open to basement with the third item being a Carbon Monoxide detector. From your posts the concern you seem to be conveying without stating it outright is the point of having two items in conflict, ie: A/C set for cooling down to 72F and furnace perhaps set for 72F and both running while you're out shopping. Could you adapt a 3 position switch to handle both items as thermostat and furnace are both low voltage. Perhaps, at worse case scenario, a couple of small relays would need to be employed in concert with 3 way switch so that you have power to only one thermostat at a time?
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Old 11-26-2007, 05:13 PM   #9
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I have dealt with commercial HVAC and set points. An example is the Honeywell Chronotherm thermostat. It is not possible to run both the AC and heat at the same time the thermostat locks it out but....it will cycle back and forth every few minutes from heat to cool if the set points are to close. IE 72 for heat and 72 for cool. I think the key to this whole thing is this....turn off one before you turn on the other. I am sure you could employ some type of three way switch that would swap the power from one thermostat to the other if you really wanted to spend the time at the fuse pannel to wire in a 3 way switch. A simple ON-OFF-ON would work to send 12v to the furnace thermostat and then 12v to the module located in the roof AC unit. But then we are adding an "ugly" switch in the wall next to the thermostats. For me I think its just a matter of keeping one off while the other is on. Worst case you run up a whopping bill for electric and burn off a bunch of propane as both units are on...LOL
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Old 11-26-2007, 11:50 PM   #10
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I've been thinking about doing this very thing (installing a separate setback heater thermostat) but I'm not sure if a standard Lowes/Home Depot unit will work. All the thermostats I've looked at are 24V and millivolt. Will those work on the MS? I'd be interested to know how this works out for you.
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Old 11-27-2007, 03:43 AM   #11
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I picked up a Hunter 44260 ($31.00 clearance Lowes #126339) thermostat 7 day (5+1+1), 4 programs per days. It works flawless and I couldn't be happier. It took about an hour to install. You have two blue wires off the furnace those go to one white and one orange wire. If you follow those back they run up the chase (where the water heater paddle switch, slide out controls and scare lights are mounted to) to the ceiling. I chose to cut those wires at the furnace and pulled them back to behind the removable panel that at the bottom of the chase. The factory wires have wire ties that hold them to the ABS vent in the chase so you cant pull them up or really use the existing wiring very easy. I then took out the slide switch panel and that gave a ton of room to get my hands and to snake some 18/2 lamp cord down the chase. Routed it back to the furnace and used pigtail connectors. I then drilled a 3/8" (really I just smacked my magnetic screw driver end through..lol) the luan paneling to mount the new thermostat right above the old one. The Hunter thermostat I picked was just a tad to large to fit between the CO monitor and the 5 button. So I picked above and chose not to move one of the others to make room. I spaced it out so it looked right. I might tend to wonder about the ability to keep the temp even in the whole cabin but worse case is (like my Avion now) I have to set it higher than you would think to make the whole place warm. In my Avion the thermostat sits above a heat duct so it always turns off early. Just seems so odd to have to set it to 74 to get it to 69-70 in the cabin...lol. Anyways you just connect two wires to the thermostat (I used the blue 12V from the furnace to the ribbed lamp wire and connected that to the Hunter + side (side with the jumper) and connected the other wire, for a two wire install. Install batteries and set it. Works great so will any 24v-millivolt thermostat with batteries will work.
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Old 04-29-2009, 06:06 AM   #12
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You should be able to instal a heat pump capable, programmable thermostat in place of the one controlling the heat pump now. It would be a matter of figuring out which of its wires to connect to the W terminal that activates the gas furnace. All the furnace controls would also need to be connected to the common from the transformer feeding the heat pump controls. If the heat pump isn't using the furnace blower as its air handler, you will need to run wire between the 2.

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Old 04-29-2009, 08:11 AM   #13
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" I just can’t believe DT didn’t even seal the plastic trim piece".

If you keep looking, you'll find other examples of when Doubletree was apparently operating without a Quality Control process. The '05 and '06 models seem to be worse than others. Welcome, and thanks for your input.

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Old 05-04-2009, 10:24 AM   #14
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I have been thinking about doin the same thing.. seperate thermostat for furnace. because the warm days need AC and the chilly nights need a tiny bit of heat. I hate to use propane when AC is free but it is such a little bit I could live with it. I could set the furnace for 71 and the AC for 76 and have automatic switching... not that oldtimers disease causes me to roust my chilled old but up at 3 am to turn on the heatpump or anything. LOL
keep on truckin
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Old 10-24-2009, 07:08 AM   #15
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OLD DIRT????WTF
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Old 10-24-2009, 09:10 AM   #16
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Stupid spammer.
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Old 10-26-2009, 10:08 AM   #17
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Gone

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Old 11-10-2010, 09:22 AM   #18
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I think the rig MAY have one or two AC heat pump units they are not the furnace settings. Well the furnace will be labeled as furnace and the heat pump will be labeled heat. Then the heat pump setting does show up first in line after cool.
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