Blower Control

When the ignition switch is in RUN, battery voltage is applied to the heater and A/C control mode selector switch. When the mode selector switch is in any position but OFF voltage is applied to the heater and A/C control fan switch.

The fan switch and the blower resistor assembly work together to determine how much voltage is applied to the blower motor. The blower motor is a DC motor whose speed is proportional to input voltage.
With the blower switch in LO, all three blower resistor assembly resistors are in the blower circuit so the blower runs at its slowest speed.

With the blower switch in M1, the blower switch bypasses one of the resistors so the blower runs faster.

With the blower switch in M2, two of the resistors are bypassed so the blower runs even faster.

In HI, the blower switch bypasses the blower resistor and supplies voltage to the blower relay coil. The coil energizes and the relay contacts close. Battery voltage is supplied directly to the blower motor and it runs at maximum speed.