This is probably an issue with the blower motor for the front HVAC vent system. The blower motor is the devise that your car uses to blow air through the vents which you control with the fan speed control. The vehicles electricity is passed through a series of resistors, which cut the voltage going to the blower motor depending on what amount of air you would like to come out of the vents. For instance if you want the maximum amount of air coming out of the vents, then the electricity in the circuit might completely bypass the resisters in the circuit, and supply a 12 volts to the blower motor, making the fan in the blower motor operate at 100%. If you choose low on your fan speed control, the electricity going to the blower motor will have to pass all of the resistors in the circuit, cutting the voltage down to , let's say, 6 volts, and the fan in the blower motor will only operate at 50%, and so on.
I have included a link down below for you to go to.
I have also included some more specific vehicle tests and the HVAC wiring diagram in the diagrams below. Please go through this information and get back to us with what you find out.
Tuesday, March 12th, 2019 AT 3:27 PM