HVAC Blower Controls Circuit Description

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

The fan switch and the blower resistor assembly work together in order to determine the amount of voltage that is supplied to the blower motor. The blower motor is a DC motor whose speed is proportional to the input voltage.

With the blower switch in LO, the following actions occur:
1. All 3 blower resistors are in the blower circuit.
2. The blower runs at the slowest speed.

With the blower switch in M1, the following actions occur:
1. The blower switch bypasses 1 resistor.
2. The blower runs faster.

With the blower switch in M2, the following actions occur:
1. The blower switch bypasses 2 resistors.
2. The blower runs even faster.
With the blower switch in HI, the following actions occur:
1. The blower switch bypasses the blower resistor.
2. The blower switch supplies voltage to the blower relay coil.
3. Battery voltage is supplied directly to the blower motor.
4. The blower runs at maximum speed.