RV Repair: AC & Furnace, furnace blower, hydroflame furnace

Question
Both my AC and my Furnace will not work in either the heating or cooling mode, nor will the fan run on the AC.  The AC is 110V and the Furnace is 12V, the only common they share is the thermostat.  What should I check to find the problem?  All of my fuses and breakers are OK.  

Answer
Jeff,
    The first thing to check would be to see if there is a fuse on the back of the t-stat.  If there is not or it's okay then check to see if it has a Hydroflame furnace.  If so you will want to open the outside access panel to it and see if the breaker mounted on the furnace is tripped or off.  If it's not tripped or off then I would begin to suspect that the t-stat has gone bad.  To confirm this you can remove it from the wall and look at the wiring.  You should have a set of two wires and another set of 4-5 conductor for the a/c.  The two conductor set (probably red and white) are for the furnace and also usually provide 12 volts for ducted roof top a/c's.  You should be able to hook the red and white together and after 30 seconds or so the furnace blower should come on.  If it doesn't come on then you either don't have 12 volts to the furnace or it has something failed on it.  With a meter or test light check with 1 lead to ground and 1 lead t the red/white wires 1 at a time.  The red should be live but sometimes they get switched.  If one of those has 12 volts but the furnace didn't come on it's something internal to the furnace.  Check these out and let m know what you find and we will go from there.  Good Luck.

Darren