Trouble Shooting your Car’s Blower Motor Resistor

In most cars, the Blower Motor Resistor is located near the Blower Motor. The Resistor is used

to control the speed of the Blower Motor in cars with the Manual heating and Air Conditioning

system. It contains three or four separate Resistors built into one unit. The Motor speed is

controlled by the fan switch which changes the voltage and current applied to the motor by

changing the number of Resistors connected in series with the Motor.

The procedure for testing of Blower Motor Resistor testing may vary in different Cars.

According to the service manual for this particular vehicle specifies that the resistance between

certain terminals.

The Resistor could be measured and compared to specifications according to the vehicals

manuals, the resistance between these two terminals should be close to 1.0 ohms (1.0 Ω). It

measured around 1.9 megohms (1.9 MΩ) while checking , which means this resistor is bad.

When inspecting if you find some corrosion spots at one of the corners then the faulty Resistor

must be replaced.

The most common symptom of a failed Blower Motor Resistor is when it doesn’t work at lower

speeds but works at the higher speed settings. Any mechanical resistance to the Motor rotation

will cause excessive current draw in the circuit, the excessive current can overheat and

prematurely damage the Blower Motor Resistor.

The problem must be properly diagnosed, sometimes, the Resistor may fail when there is some

mechanical resistance to the Motor rotation; for example, if the motor fan blade is jammed by

some foreign objects such as leaves or the Motor bearings are wearing out.

However, if the Motor doesn’t work in some speed settings but works in others, it does not

necessarily mean that the Resistor is bad. Issues with the connectors, wiring or the switches itself

can also cause the same symptoms.

If the Motor doesn’t work at all, many other things can go bad including the Motor itself. In

some Cars, it’s very easy to replace, in others the access might be difficult.

You need to know the various symptoms of a bad Blower Motor Resistor, to diagnose the

problem accurately.

Troubleshooting of Blower Motor Resistor is usually beyond the abilities of a do-it-yourself

because it often requires specialized training and tools. In case, you are not confident about

pulling off this procedure, take the help from a Car mechanic.

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