Dometic ac won’t run. All voltage present. Loose 12volt when thermostat is connected! 12volts present when thermostat is disconnected! Iv replaced the thermostat and control board but the problem remains! What should I do??

SOURCE: Goodman GMP075-3 ignition problem

bad board,i have had several board failures on goodman

Mike Butler

• 6674 Answers
• Posted on Jul 08, 2009

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.

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

Kelly

• 3740 Answers
• Posted on Apr 17, 2010

SOURCE: Dometic RM3801. Propane ignition failure.

The older units has a 3 VDC glow coil the newer units have a 12VDC igniter.

Fromwhat your described above the next paragragh is your ignition system.

The igniter control voltages in the newer SPARK type igniters are (+) = 12VDC, (L)= high voltage lead (Spark plug voltage! I.e ruin your meter type voltage), (-)= Ground L is the lead that passes the HV spark from the control unit to the ignitor plate. The L lead should pass one heck of a hit if is workng correctly.
If not look at the HV lead to see if it is grounding out somewhere.

If the gas safety valve is not sensing gas pressure... you will not have 12VDC to the + terminal of the ignition moudule.

With the gas on and you have 12VDC at the ignition module + terminal then most likely the ignition module is bad.


Kelly

SOURCE: RV Dometic Duo Therm roof top AC w/heat pump Model

If the Air comeing out is the same as the temp inside the RV make sure the compressor is running and not just the fans. It could be low on freon. If freon is ok then you would need to ck the wiring to the selector switch for a short. It would be obviouse because there will be melted wires. I am leaning toword low on freon since you have already been inside the wiring/control unit.

SOURCE: My Dometic AC on my travel trailer cools well but I cannot set the fan to stay on when the compressor cycles off. Can a different switch or board be installed to allow the fan to stay on?

An energy saver setting is what it sounds like. Turn off energy saver feature and fan should run 100% and compressor cycle on-off separately.If not familiar with energy saver setting .make sure it has one or not before disregarding this.