How to test a blower motor resistor block?
CASE 1: Continuity exists between all the blower motor resistor terminals. This is the correct and expected test result. If there isn’t any burn damage to the resistor’s coils or its connector, then you can conclude the blower motor resistor block is OK and not defective.
What happens when you heat a blower resistor?
Blower resistor terminals can develop resistance, and when they do, they get hot and begin to oxidize even further, creating large amounts of resistance where no resistance should be, heating the wire terminals and the wires feeding them until they scorch and melt the blower resistor connector.
How is a step resistor used in a fan?
A voltmeter connected to both ends of a resistor while current is passing through it to a load will measure the amount of voltage being “dropped” by the resistor. Because lower voltage means lower current delivered to the fan, the stepped resistor circuit can be used to control fan speed.
What happens when a resistor block is defective?
If the resistor block is defective, you’ll get a no-continuity test result when testing across the indicated terminals. This means that your multimeter will read OL if there’s no continuity.
What are the symptoms of a failed blower motor resistor?
Blower motor resistor problems. Problems with a blower motor resistor are common in many cars. The most common symptom of a failed blower motor resistor is when the heater fan only runs at high speed and doesn’t work at low speeds.
How does a blower motor resistor control the fan speed?
The blower motor resistor controls the fan speed of the blower motor and the resulting change in air pressure produced by the movement of the blower fan. It accomplishes this by regulating the electric current that powers the motor.
When to replace the resistor on a heater?
If your fan speed control does not seem to work you may want to replace this fan speed control component. While the switch could have been the issue I also had a squealing blower motor and oftentimes you’ll burn up a resistor when running a squealing heater fan motor.
A voltmeter connected to both ends of a resistor while current is passing through it to a load will measure the amount of voltage being “dropped” by the resistor. Because lower voltage means lower current delivered to the fan, the stepped resistor circuit can be used to control fan speed.