2017 3791RD furnace issue

[usaf_retired]

Been troubleshooting furnace issue. Furnace works ok when jumping the 2 blue thermostat wires back towards the furnace. when I wire it back to normal i'm having a 12 volt power issue. It sometime has a delayed start after requesting heat. Blower will start up for about 2-3 seconds then shuts back down. blower might try to start up again, then does the same thing...shuts back off after 2-3 seconds. It's like it's not getting a steady 12 volts. I went on top the RV (rear unit) to check wiring up there. I cleaned the furnace connection to the ac control board...no help. I put a new Dinosaur control board already. called Dinosaur tech line. He says there is corrosion somewhere causing it. Anybody have a idea what the trouble could be? Thanks

[ChuckS]

If this is a CCC2 Dometic thermostat the thermostat receives 12 volts from the air conditioner electronic control module up on the roof... the wire is a 4 conductor RJ45 connection on back of thermostat and up at control module

I’d try reseating connections at CCC2 and up top on roof... the other two wires in that 4 wire line are for the CANBUS data telling control module what to do..

You stated you checked the two blue wires up top that go to furnace..did you check the joining connections on those two wires at back side of furnace where the connect to wires running up to roof unit

[Daryles]

Some people have had to change the sail switch, some have changed the black self resetable fuse in the fuse panel with a regular fuse (just for troubleshooting).
There is a furnace TS pdf in the files folder. Hope it helps.
http://www.montanaowners.com/forums/...hp?do=cat&id=3

[usaf_retired]

Originally Posted by ChuckS

If this is a CCC2 Dometic thermostat the thermostat receives 12 volts from the air conditioner electronic control module up on the roof... the wire is a 4 conductor RJ45 connection on back of thermostat and up at control module

I’d try reseating connections at CCC2 and up top on roof... the other two wires in that 4 wire line are for the CANBUS data telling control module what to do..

You stated you checked the two blue wires up top that go to furnace..did you check the joining connections on those two wires at back side of furnace where the connect to wires running up to roof unit

Thanks for your info. I did get it back up and running normal. I did redo the connections at the thermostat (swapped it with the bedroom stat) before I posted here. I pulled the 2 furnace spade connectors at the ac board up top and cleaned the posts. You mentioned the RJ45 connector up top. I didn't see that. Where is it located? The thermostat blue wires behind the furnace to where it's tied into the rv wiring connections were poorly crimped. i can see bare cooper. I can't reach that far in there to properly correct it. I don't what to pull the heater out at this time. Cold weather coming. I reached back there with a probe i have to separate the wires best I could so they don't touch.

[usaf_retired]

Originally Posted by Daryles

Some people have had to change the sail switch, some have changed the black self resetable fuse in the fuse panel with a regular fuse (just for troubleshooting).
There is a furnace TS pdf in the files folder. Hope it helps.
http://www.montanaowners.com/forums/...hp?do=cat&id=3

I already put a new sail switch. I did pull that black resettable fuse and replaced it with a regular one. Matter fact I ended up breaking the black one while pulling it out. Does it have to have a resettable one? Thanks for your info.
Oh yeah I did get the furnace running again.