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Old 05-30-2010, 05:53 PM   #1
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2010 30' Classic
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South of the river , Minnesota
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Late model Duo-Therm thermostat

I have the dual A/C setup and it has never worked right. Tore into it today not wanting to fuss with taking it to the dealer.

The thermostat is connected to the main A/C with phone wire with a modular RJ11 connector at both ends. Not a high-reliability connector under vibration. Airstream has "spliced" this -- twice -- using RJ11 extension connectors like you'd use to hook up a phone in the basement of your house. Sloppy. One was loose and flakey, and there was enough slack that I removed it.

Then there's another RJ11 cable running from the main A/C to the rear A/C. The rear A/C doesn't have its own thermostat but does have a temperature sensor in the wall, connected by a pair of wires with a molex connector.

The molex connector wasn't connected. I plugged it in and everything works.

This business of having one thermostat that is a master control for the furnace and both A/C units is a dubious benefit at best and with the flaky RJ11s I'm not sure I like it at all. Bad engineering.

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Old 05-30-2010, 06:07 PM   #2
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Naples, FL , Hood River, OR
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With your 2-zone Dometic Comfort Control Center (CCC), you join the majority of motor home owners that use the same set-up. In my experience ( I am a Dometic Team 2000 Service Center) they have proven to be the most reliable and easy to service t/stat and HVAC system in the RV industry today.

They have many more functions than just A/C and heat. Motor Homes use this system for a temperature controlled automatic generator start if the power fails and the temps drop below a user determined set point (think pets in the coach on a hot day) so the roof airs will continue to operate.

Also, the CCC will control up to 4 zones of A/C, heat pump, furnace or Aqua-Hot hydronic heating. The system generally runs from the CCC to the lead A/C unit (generally zone 1) and then has a series connection to the other units by 6 conductor data cable (like phone wire but with different plug orientations). Each roof air has a connection for the corresponding heating zone and source.

I agree that the cheap RJ-11 unions can be a problem, but if they are properly installed with strain relief and cabled to the inner roof joists and do not vibrate or move around, they are usually pretty reliable.

Lew Farber...RVIA Certified Master Tech...ABYC Certified Master Marine Electrician
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Old 06-01-2010, 09:10 AM   #3
Wise Elder
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2010 30' Classic
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South of the river , Minnesota
Join Date: Dec 2009
Posts: 4,020

Thanks for the insight.

I do note that RJ-11/RJ-45 receptacles vary enormously in their quality. It's mainly about the precision of molding, which in turn is affected by the service life of the molding dies. Nobody makes a sloppy die on purpose but the cheap manufacturers run them for an extra million products after they're out of tolerance due to wear. Like any plastic electronic part that's produced in volume, I guess.

It does seem to be working properly now that the sensor is hooked up.
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