Blower resistor » Resistor Guide The blower resistor is connected in series with the blower fan. This means that the current running through the blower motor, and thus is speed is controlled by the resistor value. The user chooses a suitable fan speed by using a selector to connect one of the resistors in the blower resistor pack. Blower resistors are made of several resistors with different resistances. There are also two additional circuits Blower motor, resistor: how it works, symptoms, problems In most modern cars, the blower motor resistor or the control module are installed inside one of the ducts in the HVAC system, close to the blower motor. This is done, so the resistor or a control module is cooled down by passing air. In some older cars, a blower motor resistor was installed on the firewall with the access from under the hood.