Blower motor resistor
Ford blower motor resistor
Most cars equipped with a manual heating, ventilation and air-conditioning (HVAC) system use a blower motor resistor to control the speed of the blower motor fan. The blower motor resistor is used to reduce the fan speed in lower settings (1,2 and 3). Some minivans and SUVs equipped with a separate heating and air conditioning system for the rear passengers use a separate blower motor resistor to control the speed of the rear blower motor fan.
Blower motor resistor problems
Usually, a blower motor resistor is installed inside the HVAC system so that air flowing through the HVAC system cools down the resistor. Due to constant heating and cooling, as well as with a moisture present in the air, some parts of the blower motor resistor can corrode, causing it to stop working. See the photo.
This blower motor resistor from the 2008 Ford Escape
has failed due to corrosion.
The most common symptom of a failed blower motor resistor is when the fan works in "High" speed, but doesn't work in some lower speeds. The highest speed setting may still work because in most cars in the highest fan speed settings the current bypasses the blower motor resistor (see the diagram below). In some cars, if the resistor is failed, the fan may stop working completely. Another reason a blower motor resistor may fail is when the blower motor has a mechanical problem or when a foreign object jams the blower motor fan blade and prevents it from spinning freely. This leads to increased current through the resistor and causes it to overheat and fail.
In most cars, replacing the blower motor resistor is not too difficult. For example, in the 2001 Toyota Camry, it can be done within 15 minutes, the part can be purchased for $25-45 online. The resistor is installed near the blower motor underneath the passenger side of the dashboard. In some cars (e.g. Dodge Caravan, Ford Escape), the glove box needs to be removed, to get the access.
Read about testing the blower motor resistor on the next page.