Question about Dometic Rooftop RV Air Conditioner

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I have a DuoTherm BriskAIr 13.5K BTU. The Dometic thermostat also controls my HydroFlame 8531-IV furnace. This morning, the furnace would not come on. I checked the wiring and there is no voltage at the thermostat blue wire on the furnace. If I jump 12 volts to the thermostat blue wire, the furnace works normally. Replaced thermostat; no change. I hear something clicking in the air conditioner unit when I switch the thermostat to furnace mode. I assume the A/C has a relay to control the thermostat voltage signal. Where can I find a schematic of the Brisk Air.

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  • Anonymous Jul 09, 2009

    First, thanks to both of you for taking the time to reply--very helpful info. This is in a 1999 Dutchmen 5th wheel. The thermostat is a Dometic analog 1999-year model p/n 3107612.008. The A/C is a DuoTherm 59516.603. I convinced myself the thermostat had failed, so put in a new one. No change. Then I found a wiring diagram for the HydroFlame 8531-IV, and used a multimeter to test the system. There is no voltage coming in at the thermostat wire (blue wire) in the furnace. If I jump 12-volts from either terminal of the furnace 10-amp circuit breaker to the blue thermostat wire, the furnace comes on, and operates normally. So the problem goes back to the thermostat circuit. A/C, fan auto/on, fan high/low: all of these work normally. When I switch to furnace mode, and move the sliding temperature control, I hear a single clicking noise from the roof unit (not the normal click from the T-stat.) Is there a relay for the furnace in the roof unit control box?? No voltage on furnace thermostat blue wire means furnace doesn't come on--put 12 volts there and it works fine. Trying to find out more about how the roof unit interacts with the thermostat & furnace.

  • Anonymous Sep 27, 2009

    When I finally got time to pull off the cover & the lid from the A/C unit, I found a disconnected wire in the HydroFlame thermostat circuit. By all means download the repair manual from Bryant RV, if you are trying to repair a similar problem. Turns out that there are 2 blue/white striped wires from the Roof Unit relay box which are attached to 2 small wires which run directly to the HydroFlame heater main connector terminals 2 & 5. These are the 2 "blue wires" inside of the heater unit I talked about in my earlier post. These two wires are the thermostat circuit for the heater...and they do NOT attach to the main control thermostat inside of the trailer. The main control thermostat has about 7 small colored wires (inside of an insulated sheath) which run to the relay box on the roof unit. When the thermostat calls for heat, the small white wire from the control thermostat causes a relay inside of the roof unit box to activate, connecting the two heater T-stat wires together. I drew a wiring schematic based on the info from the Bryant RV manual, and put it with my Dometic manual.

  • Anonymous Mar 18, 2014

    When selecting the furnace setting the air conditioner also turn on what is the problem? This is A Dometic Single Zone Thermostat



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Mike Butler

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If you look at control box at roof unit, they usually use a separate set of wires for furnace. See what colors they are attached to at harness to thermostat. Some just follow other harness, and come out at thermostat. (bypass control box) Once you've determined which 2 they are, join them together & see if furnace starts, as it should. If it does, thermostat is faulty. If not, pull outside cover off & check voltages at furnace. I'm guessing by furnace model that your unit is approx 30 ft , but if it's a park model, you may have 24 volt system on furnace or 12 volt. Another way of confirming is to go to back of furnace where air intake grille is inside your unit, and locate 2 blue wires going to furnace & remove whatever wires are attached to them & connect them together. Furnace should start up.

Posted on Jul 08, 2009

Testimonial: "thanks for the link. info solved my problem."

  • Mike Butler
    Mike Butler Jul 09, 2009

    Here's a link that may very well come in handy for you. It's an excellent PDF file, service manual for dometic AC & thermostats. When you get there, scroll to pages 47-54. I think you will find these helpful.




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What kind of a thermostat is this? I am assuming that this the standard Analog Dometic Thermostat with the wires that connect to a bar across the top. I'm not sure which blue wire for the furnace you are referring to at the thermostat. The blue wire at the thermostat is the -12VDC wire or ground for the unit. The white wire on the thermostat is the one that calls for heat. The white energizes and the relay on the board makes to connect the two furnace thermostat wires together causing the furnace to fire.

Posted on Jul 09, 2009


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