How The Blower Motor Resistor Works

resistorsThis figure shows how the blower motor resistance is connected in a typical car. In this car, at the highest "4" fan speed setting, the resistor is bypassed and the radiator cooling fan is powered directly by the fan switch. This is why in some cars if the resistance is bad, the blower motor can still work at the "high" speed setting.

In this figure, the fan switch is set to speed "1", so the ac blower motor current is reduced by three resistors (R2 + R3 + R4) connected in series. The current is shown in blue and red.

In setting "2", there are two resistors in series, while in "3", there is only one resistor.
Adding resistance to the circuit will reduce the current in the circuit. When several resistors are connected in series, the total resistance increases and is equal to the sum of the individual resistances.

Post time: Jul-06-2020