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I've been going round and round with Airxcel tech support on this subject and am getting a bit frustrated with them, so I thought I'd drop the question here: I have a Coleman Mach roof A/C unit that's ~10 years old. It works well generally and is controlled with a mode selector switch as well as a manual thermostat dial. My unit has a simple, add-on heat strip which comes in handy for cool weather camping, and the heat function is activated by turning the mode selector switch to "Low Heat." The problem is that, when using the heat strip, the thermostat dial doesn't seem to have any bearing on its function—the unit just blows warm air constantly and always pulls about 12A, regardless of the thermostat setting and regardless of the ambient temp in the RV. That can get real toasty, real fast, in a tiny RV! And that is not how it was designed to work; the thermostat is intended to turn the heat strip off and on, in order to maintain a set temperature of course. The question is, "Why is it not working correctly?" If you look at the highlighted portion of the attached wiring diagram you can see that, in Low Heat mode, the hot/black wire is always connected to the Heater Plug. Then, when the thermostat is calling for heat, the white/neutral supply wire makes a connection to the blue wire, which is the other side of the circuit at the Heater Plug (in other words, it's designed to switch the neutral off/on, rather than switching the hot). I have tried completely replacing the thermostat, which didn't help at all. I then tried pulling the blue wire completely off the thermostat, left it dangling... and the heat strip still continued to burn merrily away! Bottom-line, it appears that the heat strip circuit is being completed via another path, bypassing the thermostat somehow and making it irrelevant. Which seems dangerous. How does this happen and what's the fix?