2005 GMC 2500hd pickup truck, HVAC blower speed controller/relay connector got hot, burned out connector and wire, lots of smoke. It happened when turn fan to high. The failure was due to contact resistance at the connector. The wire harness end is tinted copper, the relay/controller connector is bare metal. Due to galvanization of different metal in the connection system, the connector is undersize for the black wire, which is the return current because the blower assembly is plastic. The resistance between the contact point of the connector act as heater and got hot, burn out connection and connector housing. The speed control unit, which composed of few power resistor is mounted in the air stream that it will collect vapor water due to condensation when ac is in used. This cause corrosion in the speed controller/relay board. The work around is bypass the connector by shorting the black wire from the blower motor to the black input wire that burned out. Cut the input black wire, wire nut it together with a 12 awg jumper wire, cut the black wire at the blower motor, wire nut it to the other end of the jumper wire. After the jumper put in, blower fan works in all speed and no smoke from connector and wire.

- Mayfield Heights, OH, USA