I needed a system reset on my Mitsubishi top of the line multi zone and they said the temperature had to be above 50 for the reset to work. What a bunch of s---h. Buy a unit that says it'll work to -15 which it does and produces heat @ 115 degrees but can't run long enough to produce enough heat without having to defrost. I've had it several years and to be honest once it's zero it's pretty much worthless. Mike