I.What is blower motor resistor ?
The Blower Motor Resistor (BMR) is an important component in an automotive heating, ventilation and air conditioning (HVAC) system. Its primary function is to control the speed at which the blower (also known as the fan) operates.
The blower motor resistor adjusts the speed of the fan by changing the amount of electricity flowing through it. When you adjust the speed of the fan in your car, you are actually changing the resistance of the resistor , which in turn changes the amount of current, which in turn controls the speed at which the fan runs.
In some models, the blower motor resistor may contain a thermistor that prevents the blower motor from overheating by reducing the current when the motor overheats.
II. Principle of operation of blower motor resistors
A blower is a mechanical device that utilizes a motor to drive a rotor to rotate and produce an airflow to feed gas into a heating furnace for combustion. During the working process, the blower needs to heat and dry the gas to a certain extent, which needs to adjust the air temperature and humidity by controlling the resistor.
Blower resistance is an electrical component that converts electrical energy into thermal energy, and its main principle is to heat the air through the resistance heat generated when the current passes through the resistance, so that it can reach the expected temperature and humidity. Resistor is a kind of component with fixed resistance value. According to different electrosensitive materials and molding process, the resistors produced have different resistance value and power, which can meet different resistance requirements.
III. Role of the blower motor resistor
COMFORT: The blower motor resistor controls the speed of the blower (fan), which affects the air flow in the vehicle. It allows the driver and passengers to adjust the fan speed as needed to ensure comfort inside the vehicle.
SAFETY: In freezing weather or wet conditions, the blower motor resistor can help clear windshield fog or defrost by adjusting the speed of the blower to improve driver visibility and vehicle safety.
ENERGT SAVINGS: By allowing the driver to adjust the blower speed as needed, the blower motor resistor can help save energy by allowing the blower to run only at the speed needed when needed.
PROTECTING EQUIPMENTS: In some models, the blower motor resistor may have a thermistor that protects the equipment from damage by reducing the current to prevent the motor from overheating when the blower motor overheats.
IV. How to test blower motor resistors
- Locating the Resistor: The resistor is usually located near the blower. It usually has a connecting plug and is connected to several wires. If you are unsure of the location, refer to your vehicle's service manual.
- Disconnect the Resistor: You will need to disconnect the resistor before starting the test. First, make sure the car's power is off. Then, locate the resistor's connector, press the locking clip, and pull the connector out.
- Set the multimeter: You need to set the multimeter to measure resistance (ohms).
- Connect the multimeter: Connect the probe of the multimeter to the connector of the resistor. Note that different resistors may have different connections, so you may need to refer to your car's service manual.
- Compare readings: Check the reading of the multimeter and compare it to the specifications provided by the manufacturer. If the multimeter reading does not match the specifications, the resistor may be bad.
- Repeat Test: To ensure accuracy, you may need to repeat the test at different speed settings.
Note: When measuring the resistance, you need to turn off the car and disconnect the power beforehand, otherwise the error of the measured resistance will be bigger, and if the current is too high, it may burn the multimeter. If the current is too high, the multimeter may be burned out. If the operation is not careful, there is also the risk of electric shock, which affects the personal safety of car users, so be careful when measuring.
