If you look in the manual you will find that position 1-3 and position 4 BOTH have a fuse.
Try replacing the fuse for position 4...
If the blower only works on high the blower resistor is most likely the problem and should be replaced. On rare occasions if the car has blown the resistor more than once the blower motor shouuld be replaced.
Same problem on mine...I had the blower motor module replaced and it works great.
Defective blower motor resistor pack.
When you find out let me know I have same problem replaced blower fan and resisitor did not work. I have a blazer zr2 2002
Typically a relay or resistor. But could be a blower switch or blower motor problem.
I had the exact same problem with a 1999 Dodge Stratus. I replaced the blower motor resistor twice only to find out that the blower motor itself was the problem. I know others with the same type of car, i.e. Dodge Stratus that had this problem. It turns out that Chrysler must have gotten a bad batch of blower motors form some supplier. I went to the junk yard and got another used blower motor and put that in with another resistor (the second one blew out again) and it worked fine!
If the heater blower has humming noise when motor is running, first check its capacitor. If the capacitor is fine, then the motor is the problem and may need to be replaced.
As for why it blows only on the high speed you most likely will have a bad blower resister and for the noise, it could be a bad blower motor, bad blower wheel or trash that is stuck in the blower wheel or housing.......
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.
My blower would blow cold air at idle & engine would start to overheat, I replaced my thermostat & problem solved.
The replacement may have been bad. There may also be a problem with the relay from the AC blower to the fuse box.
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