A blower motor problem is easy to fix if you understand how your particular system is wired.
Here are the blower motor fix steps:
Please check and confirm that if you have a manual or automatic heating system in your vehicle?
Do you set the temperature and the system keeps that temperature or do you have to adjust the temperature up manually and then turn it down once the cabin heats up? Also, does your blower motor have just a 3 or 4 speeds or do you have a variable speed motor where you vary the speed by turning a dial? Why do you need to know that? Because most automatic systems use an electronic motor controller while manual systems usually use a blower motor resistor to obtain 3 or 4 different speeds.
What is a blower motor resistor?
Heating systems with just 3 or 4 speeds use a motor resistor along with the speed switch to regulate the motor speed. The resistors are arranged in series to reduce the voltage in steps, depending on where in the series you apply power.
Blower resistors can burn out. When that happens, you lose that speed. So you may have high speed, but no lower speeds.
What is a blower motor controller?
A variable-speed motor is controlled by a digital speed controller. In most cases, the controller receives a digital input from the speed switch or HVAC control head. The control head then sends a command to the motor controller to change the speed to the driver’s preferences. To obtain the requested speed, the motor controller rapidly pulses the ground circuit on and off. So a half-speed driver request will result in the blower motor controller pulsing the ground connection off twice as often as when the fan is running at full speed.
Blower wiring diagrams for three or four-speed systems
Carmakers use these three common wiring methods to supply power and ground to the blower motor in a manual system using a blower motor resistor. In one design, the carmaker supplies battery power to the speed switch, which switches the power to the appropriate connection on the blower motor resistor. In those applications, the motor resistor reduces power for the slower speeds and the blower motor has a permanent ground connection to complete the circuit. See the wiring diagram for that setup below.
Or, carmakers can supply power to the motor and control blower speeds on the ground side of the circuit. See the wiring diagram for that setup below
Or, carmakers can opt for a motor resistor AND a high-speed relay. See the wiring diagram below for that setup.
Blower motor wiring diagram for variable speed systems
Variable-speed blower motors don’t use a blower motor resistor. Instead, they use a blower motor speed control or a power transistor. Variable speed motors are most often used in vehicles with automatic climate control. In those applications, the HVAC control head is a digitally controlled unit and uses various sensor inputs to determine when to supply heat. Based on the driver’s input to the blower speed switch, the HVAC control head sends a digital signal to the blower motor speed control module. The module uses that information to pulse either power or ground to the motor.