Be sure the motor is getting a good ground is the first thing, second, get rid of the 110V house switch. Make sure the motor is wired correctly, some have two power wires ( high & low ) and ground through the case. Did you bench test the motor? Any good 12v fan should blow really hard on high, how do you regulate the speeds? All heaters should have a 2 or 3 speed setting? Call the vendor and ask about wiring the thing, and go ahead and get a good switch while on the phone. Joe
