Blower Motor: Description and Operation

Blower Motor Speed Control





Heatsink assemblies are mounted in the outlets of the blower motor units and consist of: an interference suppressor, feedback isolation diodes, and power transistor. The units are fed via an ignition switch controlled fuse, and an isolation relay which is mounted within the blower motor assembly.

On all fan speeds except high and defrost, the negative circuit for the fan motor is via the power transistor and the HCM. The feedback diode enables the HCM to sense the voltage at the negative side of the fan motor and so calculate the fan speed. With the fan motor switched to high, the high speed relay is energized giving the motor negative circuit a direct path to earth via the relay contacts.