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Old 05-21-2019, 03:09 PM   #1
RV6A
Seasoned Camper
 
Join Date: Mar 2017
Location: Pine
Posts: 53
M.O.C. #19552
Duo Therm Comfort Control is dead

Help,

2009 Montana with single air and furnace. We have only run the furnace one night many years ago and the AC has never been on. We have always heated with a stand alone unit that is vented outside and has no fan to run the batteries down. Works great as it is 40,000 BTU.

The problem is I tried to start the furnace today as I get ready for the upcoming trip and it's 33F in and out of the trailer. There is also 12" of snow covering everything.

The Duo-Therm 5 button Comfort Control has a dead screen. No heat, no AC, no nothing, just a dead screen.

It seems that a tele cable is used between the thermostat and the AC unit. Another tele cable then heads from the AC to the furnace.

The AC needs 12 volts for some reason and as far as I can tell there is not any 12V power going to the AC. I checked all the fuses in the 12V fuse block and they all Ohm good.

Any suggestions? I'm thinking that a mouse may be involved.

Can the furnace be controlled by a simple mercury T-stat?

This is the first real problem we have had with our Montana.
 
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2009 3075RL; Modded to our taste.
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Old 05-22-2019, 09:36 AM   #2
ChuckS
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Join Date: Dec 2017
Location: Mountain Home
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M.O.C. #20949
The CCC2 thermostat gets its 12 VDC power from the roof mounted air conditioner electronic control module. 12 volts is always present at the module when battery or shore power is on. The module most likely is getting its DC power off the DC fuse in power center panel labeled kitchen.

The overhead power fan and vent cover is what is on that circuit and Keystone piggy backed into this line most likely at the top power vent. Remove inside shroud from roof fan to verify.

You can also remove air conditioner shroud and verify if you are missing 12’volts at
Control module. The module sends DC power down to CCC2 via RJ11 phone cable. Red and
Black wires on phone cable carry the power.

Could be break in phone cable or break in DC supply wire to ECM.
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Old 05-22-2019, 09:43 AM   #3
ChuckS
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M.O.C. #20949
Pins 5 and 6 on air conditioner electronic control module at P6 connector must have 12 VDC present all the time. If no power here troubleshoot down stream to find break in wire

If power is present then verify red/black wires on telephone line have 12 VDC. If not either bad telephone cable or ECM
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Old 05-22-2019, 11:19 AM   #4
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Quote:
Originally Posted by ChuckS View Post
Pins 5 and 6 on air conditioner electronic control module at P6 connector must have 12 VDC present all the time. If no power here troubleshoot down stream to find break in wire

If power is present then verify red/black wires on telephone line have 12 VDC. If not either bad telephone cable or ECM

I do have 12V to the AC and the 3 Amp fuse is good. The control center is not receiving 12V so it is either the tele line or ECM as you state.



No time to further troubleshoot today but I'll take equipment to build a tele cable for testing sometime this weekend. I'm hoping it's the cable and not the ECM.
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Old 05-23-2019, 09:37 AM   #5
ChuckS
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M.O.C. #20949
Be sure and correctly wire the RJ connections. One end is flipped so tab will make a standard 4 wire telephone cable be wired backwards.
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Old 08-21-2019, 12:39 PM   #6
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Success

Closure to this mini-thread.

Since we'll be heading to hotter climates in the near future I thought it would be nice to run the AC if needed.

I had previously checked everything I could think of and gave up. Today I tried again.

What I found is the ground wire for the 12V feed to the AC was an open circuit, no ground. I temporarily grounded the 12V Ground to the frame and low and behold the Duro Therm lighted up and I could run the furnace. Since I don't have enough power, 15 amp from the house, I can only assume the AC will work.
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Old 08-25-2019, 08:25 AM   #7
ChuckS
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M.O.C. #20949
Glad you located break in 12 VDC from air conditioner control module to thermostat.

With a 15 amp service you can at least turn on the fan on each AC unit... one at a time to verify thermostat is now controlling the AC units.
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Old 09-04-2019, 02:07 PM   #8
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Quote:
Originally Posted by ChuckS View Post
Glad you located break in 12 VDC from air conditioner control module to thermostat.

With a 15 amp service you can at least turn on the fan on each AC unit... one at a time to verify thermostat is now controlling the AC units.
I figured that out on my own and the AC fan would run. I know this sounds strange but we have never had the AC on and only used the furnace the weekend after we brought the trailer home as we stayed in it for a test run. I have a 30K BTU vented propane heater (no fan) to keep us warm in the fall/spring. Most of our camping has been "Dry" so the less battery powered items the better. I installed two Battle Born 100 Amp hour batteries last year, what a difference that made. Next is solar on the roof.

I spent the Holliday weekend in 95-100F temps and the single AC worked. With all the blinds closed and the AC running full blast the interior stayed in the mid 70's with the big vent on the AC open. I closed the big vent to feed air to the bedroom in the evening and the cool blast from the ceiling was nice. Since I was gone all day all I wanted was the trailer to be livable when I returned in the afternoon. It worked great.
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