I’m an electrician by trade but i have a friend who needed his blower motor replaced. The parts store sold him a motor but it only has one hot leg. The control board has a hot for cooling and a hot for heating. What would happen if I wired them both together to the hot for the motor? I’m afraid back feeding the control board might fry it? Any suggestions would be appreciated.
It'd be fine, simply because I can't think of a 120 volt AC relay that would be damaged by getting back fed power. Mechanical and solid state can both handle it as far as I know. That's not a 100% you're good though, maybe 90+% confidence?
Worst case it passes current backwards through to hot and won't be able to shut itself off, but you'll catch that during testing. Nothing should blow up.