RV Furnace does not have 12v power - not working '94 Class A

[Alaskantraveler]

I have a 1994 Coachmen Santara Class A.  I recently purchased this RV. Was told everything worked. Went to use the furnace, and it is not working. No fan, no igniter. I checked the fuses. The fridge and the furnace are on the same circuit. The fuse is fine. The Fridge has power, but it appears the furnace does not. A quick check with a volt meter shows me that the thermostat is not receiving 12v. My attempts at testing the 4 wire/3 plug going into the furnace also show now 12v power. So it appears the furnace is not getting 12v even though it is on the same circuit as the fridge and the fridge is getting 12v.  Wondering if I may have a cut or corroded wire like OP in this post did. http://www.rvforum.net/SMF_forum/index.php/topic,48813.new.html#new  The furnace is kind of hard to get to as it is under the oven in a tight spot.  I asked the previous owner who said the furnace had been working. Trying to figure out where to start.  I would expect my thermostat to have one positive and one negative wire. The fact that it does not leads me to believe that there is no power at the furnace which powers the thermostat.  I can only see the 4 wire/3 plug connector that goes into the side of the heater. It is in a tight space, but generally this is the only plug into the heater right? There wouldnt be a large hot or ground wire around the back?  Any tips appreciated.

 

[Gary RV_Wizard]

The furnace actually uses to 12v sources. It will have a main power feed direct to the furnace board, plus a secondary 12v line from the wall thermostat, which serves to trigger the start-up process. Both have to be working to get any heat.  If you have no 12v to the thermostat, the furnace will never fire up.  You need to find the 12v source for the thermostat - rarely does it use the same source as the furnace itself.

 

[Alaskantraveler]

Fixed it. The issue ended up being a quick disconnect at the splice 12 inches from the plug into the furnace. The splice was taped up, it appears that the manufacturer did not connect the quick connect properly and the quick connect came loose over time. Glad it was an easy fix.