There's a safety interlock controlled by ign. key on and brake pedal depressed; you should hear the solenoid click near the gearshift. If not, you'll need to trace loss of power. Start w/ fuses. Blower motor speed control for all speeds other than high, are controlled by a blower resistor, usually located in the ductwork near the blower. They will eventually burn out, requiring replacement. See item #4.
If you are referring to the blower motor speed, and only the highest setting works, then the problem is a bad Blower Motor Resistor Pack.
It is either the blower motor control switch or the blower motor resistor pack. More than likely it is the resistor pack. It must be replaced or just live with it until it fails completely.
If you are referring to the blower motor speed control, and you only have one speed, then the blower motor resistor pack is defective and must be replaced.
Recommend you check the blower motor resistor.
Engineering
faulty blower motor resistor
30 amps.
Loose connection or blower motor is bad
No, there is not a resrt button.
There is only one blower motor resistor and it is located in the evaporator housing.
Replace the blower motor resistor.
It is under the dash on the passenger's side.