Dometic Digital Thermostat Conversion

[tmeserole]

This summer, I installed the Dometic 3313195 T-Stat and relay box and removed the analog T-Stat. I did not hook up the separate 12v furnace because we just needed AC. The AC works fine, but when I went to hook up the heater, I cannot get the heater to start. I set the T-Stat to furnace and there is a click in the relay box. The two prongs for the furnace do not seem to have any power coming out of them. Should I register 12v power across these two connections? Is there a way to hot wire the heater from these two wires to see if the problem is in the relay box, or my heater?

[tmeserole]

Well is was a bad connection on one of the wires. My guess was a ground wire, but not sure. I had 12V to the circuit board, but nothing after that. I thought it was the circuit board so I took it to the RV parts store. They had a tester and said that the circuit board was fine. I cleaned all the connections and crimped the female leads for a tighter fit. It fired right up after that and have not had a issue since. Thanks for the advice.

[dougrainer]

"This weekend I will check to make sure that I have continuity from the T-Stat to the circuit board. I assume that one is supposed to register 12v positve and the other will be 12v neg."

NO, You will have 12 volts at the AC control board and the other wire will be DEAD. It supplies the 12 volts BACK to the furnace to engage the start relay on the furnace. If you have 12 volts on 1 wire, just connect them together at the AC control board. Then go to the furnace input harness. There are 4 wires. 1 wire is 12 volt positive. 1 wire is 12 volt ground(neg). then you have the 2 blue wires. One will have 12 volts and the other will have 12 volts when the 2 wires are connected at the Roof AC. So if you have 12 volts at 3 wires going into the furnace your problem is IN the furnace. Doug

[tmeserole]

It is an Atwood furnace. We used it once or twice a year for the last 4 years. The trailer is an 2006 model.

I have 12 Volt power to the switch (red wire) inside the access panel. The switch is in the reset (on) position.

There is a red light on the circuit board. It is not on or blinking.

This weekend I will check to make sure that I have continuity from the T-Stat to the circuit board. I assume that one is supposed to register 12v positve and the other will be 12v neg.

[Old-Biscuit]

Do you have an Atwood Furnace?

Motor switch....do you mean ON/OFF CB switch on furnace (inside the access panel)?

That has direct power from your DC Dist Panel (Fused)
But the power can't get to motor until 'timed delay circuit' is energized.
This is part of the circuit board


Do you have an LED light on circuit board....is it blinking......what sequence?

Fault ------------------------------------------LED Indication

Internal Circuit Board fault -----------------Steady on, no flashing

Limit switch/Airflow problems ----------------1 flash with 3-second pause

Flame Sense fault ----------------------------2 flashes with 3-second pause

Ignition Lockout Fault -----------------------3 flashes with 3-second pause

[dougrainer]

tmeserole wrote:
Yep, I am sure it is a furnace issue. I connected the t-stat wires from the furnace together and nothing happens. I would have expected at least a small spark. At this point, I will believe that the T-Stat is working properly. I do have 12 V power to the motor switch, but I do not know what is the next step.

AS Chris stated, the AC control board does NOT produce anything for the furnace. ALL it does is, flow thru the 12 volt positive from the furnace and back down to the furnace. So, if you connected the 2 wires and nothing happens, your problem is AT the furnace system. Either the furnace fuse is blown at your 12 volt fuse center or the furnace relay system has a problem. Doug

[tmeserole]

Yep, I am sure it is a furnace issue. I connected the t-stat wires from the furnace together and nothing happens. I would have expected at least a small spark. At this point, I will believe that the T-Stat is working properly. I do have 12 V power to the motor switch, but I do not know what is the next step.

[time2roll]

Did you check the fuses? Does one of the furnace wires have 12v?
I think you can connect the wires to each other and the furnace should run.

[Chris_Bryant]

The 2 leads are just to a relay- one of the leads has to be fed 12 volt power to get it back out to the furnace. It should have been that way with the analog, as well.