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Old 10-04-2020, 05:58 PM   #1
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Dometic Duo Therm 5 button thermostat/zone 2 issue

We have a 5 button Dometic Duotherm Thermostat, 2 penguin 630516.321 heat pumps.

In trying to narrow down why zone 2 isn't showing up on our thermostat, we have tried the following:
1. Sprayed cleaner on all ends of all phone like cables (comm cables)
2. Replaced all connectors on ends of all phone like cables
3. Measured voltage between black and red on the phone like cable on unit 2 and it showed 4.75 volts. Unit 1 showed 4.75 volts also
4. Measured voltage between all wires on ccc end of phone like cable and got the following readings (polarity may be different - just wanted to see what voltage was):
Black to red - 0
Black to yellow - 40 millivolts
Black to green - 12.3 volts
Red to yellow - 0
Red to green - 12.8 volts
Yellow to green - 11.5 volts
Unit 1 works fine - but not seeing unit 2
Made a phone like cable and did the following:
1. Hooked it up from the ccc to unit 1 and it worked the same, still no zone 2
2. Hooked it up from the ccc to unit 2 and it didn't show up at the ccc at all
3. Hooked it up from unit 1 to unit 2 and unit 2 still didn't show up.


Does anyone know if the voltages on the ccc are correct and if the red/black voltage on unit 2 is high enough to make it work. Does anybody have any suggestions of things to try? We really thought it was probably one of the connectors or the cables, but that evidently isn't the case. Can we swap out the control boards on the 2 units and narrow down whether it's a control board issue? If so, and the control board is bad, can we even get a replacement control board?
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Old 10-04-2020, 06:52 PM   #2
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Have you done a reset of the thermostat?

The control boards can be swapped with each other. The DIP switches would have to be changed to correspond to the new board position, i.e. the rear board will have one set of DIP settings the front will have a different setting of the DIPs. I am going from memory as I do not have the installation manual in front of me.
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Old 10-04-2020, 07:41 PM   #3
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Have you rebooted the board by removing the fuse from the back of the thermostat and replacing it not with a new one but just replace the old one back in there . I had problems like this and that solve the problem.
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Old 10-04-2020, 07:53 PM   #4
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Yes, we have tried the hard reset on the thermostat multiple times. I wasn't aware there was a fuse in the thermostat? We had it apart, but didn't see a fuse. Where is it located?
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Old 12-21-2020, 08:34 AM   #5
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My Rig was doing the same thing...I have reviewed the thread and I am going to try some of these recommendations..I could not turn on anything on zone 2 as well.. Also, my thermostat when set to 70 would keep the front at about 90 deg F... I understand that the reset also addresses this as well.
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Old 12-21-2020, 08:49 AM   #6
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Looking at your diagnostic steps with the new com cable, I would suspect the control board. Try the board swap.

Now, the following is only speculation because I'm not certain how the two A/C units communicate with the CCC. It may be possible that either the front or the rear board is faulty. If zone 2 receives its commands through the zone 1 unit, then the fault could be with the zone 1 board. A direct connection to zone 2 from the CCC, like you tried, would not work because of the dip switch positions.
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Old 12-21-2020, 09:04 AM   #7
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Quote:
Originally Posted by pilotsteve View Post
My Rig was doing the same thing...I have reviewed the thread and I am going to try some of these recommendations..I could not turn on anything on zone 2 as well.. Also, my thermostat when set to 70 would keep the front at about 90 deg F... I understand that the reset also addresses this as well.
Note bold.

The temperature difference may be from the location of the thermistors inside your coach which determine the temperature, not the wall thermostat. If you have a single furnace and that is what you use for heating, you can get a wide difference in temperature between the zone and the thermostat. In my coach, for example, the thermostat control is on the passenger side wall, midway down the side of the coach, but the sensor for the zone is above the drivers seat above a side window. This is generally a much cooler area due to the distance from the heat vents and the proximity to the windshield. It takes a much longer time for the furnace to run to heat that sensor.
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Old 12-21-2020, 10:05 AM   #8
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This may/may not be helpful but i just resolved this exact issue on my coach, with a different thermostat. I had to go into the setup on my RV Comfort 2 Thermostat and tell it that Zone 2 was a gas furnace, and not just an A/C unit. Attached are the steps for my thermostat, so you will need to google the steps for your specific brand.
Attached Files
File Type: pdf Zone Control reset.pdf (126.2 KB, 31 views)
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Old 12-22-2020, 05:52 AM   #9
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Solution

We swapped the boards for the 2 units and then the front unit wouldn't work - we did change the dip switches before the swap. Got a new control board and it solved the problem. All is now well. Thanks for all the suggestions.
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Old 12-22-2020, 06:09 AM   #10
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Great job and thanks for the report back. That reminds me, I need to see if I kept my old control board when I changed one of my AC units a couple of months ago. Might come in handy for someone.
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