* Faulty switch: If the switch is faulty, it may not be able to send the proper signal to the blower motor to change speeds. This can cause the fan to run at only one speed, usually the highest speed.
* Faulty blower motor: If the blower motor is faulty, it may not be able to respond to the signals from the switch to change speeds. This can also cause the fan to run at only one speed.
To determine which component is causing the problem, you can try testing the switch and the blower motor.
* To test the switch, turn the fan on and off several times. If the fan only runs at one speed, the switch is likely faulty.
* To test the blower motor, remove the blower motor from the vehicle and connect it directly to a power source. If the blower motor only runs at one speed, the blower motor is likely faulty.
If you find that either the switch or the blower motor is faulty, you will need to replace it.
