![]() If there is no voltage at the motor, the entire blower motor circuit must be tested, starting from the fuse. Things like leaves, twigs, nuts, pieces of a ripped cabin filter can jam the blade of the blower motor. If there is a voltage at the motor (at least 4-6 Volt at low speed and 12 Volt at high speed), but the motor doesn't run, the motor is bad. If there is a voltage at the motor (at least 4-6 Volt at low speed and 12 Volt at high speed), but the motor doesn't run, the motor is bad or jammed. Typically it's done by measuring the voltage at the blower motor connector when it's turned on. If the blower motor doesn't work at all, the blower motor itself must be tested first. One of the symptoms of a worn out blower motor is that it can intermittently produce a loud screeching noise when running. In this case, the blower motor must also be replaced. For example, this issue was common in older Chrysler and Dodge minivans. We have seen instances where a worn-out blower motor causes a recently replaced resistor to fail again. This means after replacing the blower motor resistor, check if the blower motor runs freely and doesn't make any noise. Sometimes, a blower motor resistor might fail due to problems with the blower motor itself. In our case the ohmmeter shows open circuit, which means the resistor has failed. How is the blower motor resistor diagnosed? In some cars (e.g., older GM trucks), a failed blower control module or processor can cause the blower motor to continue running even with the ignition OFF. In most cases when a blower control module fails, the blower motor doesn't work at all. Problems with a blower motor control module are less frequent, but it fails for the same reason: due to corrosion or overheating when the motor is jammed or shorted. For example, this happens when the fan blade is jammed by a foreign object or when the motor bearings are worn out and it doesn't spin freely. Sometimes, the mechanical resistance to the motor rotation causes an excessive electric current that can overheat and prematurely damage the blower motor resistor. In most cases, a blower motor resistor fails due to corrosion or overheating. In some cars, a failed blower motor resistor can cause a heater fan to stop working completely. The most common symptom of a failed blower motor resistor is when the heater fan only runs at the highest speed setting (4 or 5) and doesn't work at low speeds. Problems with a blower motor resistor are common in many cars. Steps to diagnoseīlower motor resistor / control module problems ![]() Signs of automatic transmission problems.How to check the engine when buying a used car.How to get the best deal on a used car?.Buying a Used Car: 10 Common Mistakes to Avoid. ![]()
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