SOURCE: furnace problem
The problem is most likely in the control module of the roof air unit. Dometic uses the thermostat to activate and deactivate a relay in the control board of the roof ac unit whiich is just visible when you remove your air intake screen. The two blue with white stripe wires are the furnace control wires.
The furnace turns on and off by the opening and closing of relay. Most likely, the furnace control relay is stuck in the on position. On the thermostate, remove the fur wire and see if the furnace quits afrer it cycles down...it does not quit right away. With the termostat out of the loop, if the furnace does not shut down, the problem is in the control box. They are not hard to replace but you must be careful with the live wiire from the 110 ciucuit breaker. If you are not comfortable with the repair, take it to a dealer. The part number is on the assembly box. They need to know if you have the heat srip option or whatever othert options our Roof AC has. If the furnace still runs with the blue/white wires disconnected, the furnace wires are shorted somewhere between the furnace and the AC control unit.
SOURCE: Black sticky residue in gas furnace vent pipe.
Unless this is some weird act of G-d, like sap from a nearby tree or something I will stick to furnace facts. LOL. Anyway, this sounds like an incomplete combustion situation. Let me explain. During the combustion process many elements are necessary to facilitate "complete combustion". If the correct combination is not met, the result will be a blackish residue. If you combine this residue with the condensation that normally occurs in the flu system, it could turn muddy or sludgy. This is can be a dangerous situation due to the amount of carbon monoxide (poison gas) nessessary to create this residue (similar to the film in the tailpipe of your car).
I would suggest calling another reputable company that offers true "combustion analysis" reports. The test takes around 30 minutes and they should be able to confirm my diagnosis. This test should cost anywhere between 100 and 200.00(US). Many times a simple adjustment to the gas valve or burner assembly will due the trick. Best of luck!
SOURCE: furnace won't turn on, off, with or without remote
We hotwired the thermostat wires and the furnace started. That told us that the problem was with the thermostat. We took our remote control to another camper like ours and our remote worked their furnace. That told us that the problem was in the ceiling control for the furnace/ac. But the man who owned the other camper told us that he had a problem, too, and was told to unplug all the electric including the battery, wait 2 minutes, and hook up again. This might reprogram the circuitboard, and voila! It worked.
SOURCE: Error code of E4 on Dometic HP air conditioner ??
16. SYSTEM RESET
a. Turn the ON/OFF switch to “OFF” position.
b. Simultaneously depress and hold the MODE and ZONE
push-buttons while turning the ON/OFF switch to “ON”.
FF should appear in the LCD display until the MODE
and ZONE push-buttons are released.
c. When a dip switch is turned on or off after initial configu
ration, a system reset will need to be done before the
Comfort Control CenterTM will recognize the updated selection. Try this. This is for the five button thermostat. Did you check the dip switches to be sure the proper ones are turned on? I need to know which stat you have 4 or 5 button. I have trouble shooting for both.
If you notice reset needs to take place after a dip switch is turned on or off. The dip switches are on the circuit board. You need to drop the lower cover. the dip switches will read in this order #1 heat strip/ #2 zone2/#3zone3/ #4 zone4/#5 furnace/#6 differential/#7stag/#8 gen start. Check this out and be careful. Turn off the stat to change dip switches. On will be toward the description. If you don't have remote start gen set the dip should not be on. If you dont have a Zone 3 the dip should not be on, etc.
Any questions feel free to post back
Thank you for using fixya
Jerry
SOURCE: I have a DuoTherm BriskAIr 13.5K BTU. The Dometic
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.
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