Originally Posted by Frost
It's a dometic brand AC unit. Oddly enough, since posting this the issue has stopped but I'm not confident it won't start again since it has done it once before.
I too find it odd that the setting the switch to on, the fan doesn't work. That would take the AC unit out as a possible cause since the fan should still run without the AC running.
That's right, what it is doing is energizing your fan wire, once you do that it sends the power to the fan relay in the unit that pulls the contactor or relay in. If the unit is running normal now, just try the fan in the on position and see if it will come on. If it won't come on it would be either the stat or the contactor relay in the unit, I don't know much about Dometic but there should be a board that the wire hooks to which will pass it to the relay. At that time if it didn't come on then jumper the red and either green or blue wire at the stat that will by-pass the stat. If it's still not coming on then it would be the board or relay(might all be one) If it comes on when jumpered then it's the stat, if not the board. Intermittent problems are hard to fine, so you need a plan when you catch it. My money is on the board, but they are costly$$$$. So you want to make sure, learned here on the forum that Dometic uses the negative wire for there units. Did HVAC most my life and never heard of that before, that's why I don't like dometic, there the only unit that is wired like that. Hope your problem stays away them damn little gremlins.....