Blower Motor Resistor: Description and Operation
BLOWER MOTOR RESISTORThe blower motor resistor adjusts the blower motor speed based on the blower motor switch setting. The blower motor resistor contains 3 resistor coils in series. The end of each resistor coil is wired to a setting in the blower motor switch. Voltage is available at the blower motor at all times when the ignition is in the run position and then continues to the blower motor resistor. The blower motor switch will allow a path to ground with the addition of 1, 2 or 3 coils in the blower motor resistor to the circuit. When the blower motor switch is in the MED HI position, the blower motor switch will add a path to ground through 1 coil in the blower motor resistor. When the blower motor switch is in the MED LO position, the blower motor switch will add a path to ground through 2 coils (in series) in the blower motor resistor. When the blower motor switch is in the LO position, the blower motor switch will add a path to ground through 3 coils (in series) in the blower motor resistor. When the blower motor switch is in the HI position, the blower motor resistor is bypassed.
The blower motor resistor has an overheating device (thermal limiter) that will open the resistor coil if the temperature reaches approximately 184°C (363°F), interrupting the blower motor operation in all speeds except high. The thermal limiter cannot be reset, and a new blower resistor must be installed if open.