Chevrolet Repair: a/c heater fan control, excessive amperage, blower motor

Question
Hello,
My van is venture 97, it has a problem with a/c heater fan control. If I switch the fan knob to # 1 and 2 the fan still OFF, but if I switch to # 3,4,5 the fan is ON.
I checked all the fuses, but all the fuse were good.
Would you give direction, what should I need to check or repair?
Thank you.
David

Answer
Your problem is most likely the BLOWER RESISTOR or less likely the fan control switch.

The blower resistor reduces the voltage going to the motor so different fan speeds will operate. On the low position the resistor reduces the voltage the most and on 4 it reduces the voltage the least. Position 5 does not go through the resistor...it supplies the blower motor with 12v to operate at full speed.

Since you say speeds 3, 4, 5, work ok, then I know the circuit from the blower resistor to the blower motor is ok.

This now leaves the resistor (which have been known to fail) or the switch. You can diagnose this by checking the circuit from the blower switch to the blower resistor. Positions 1 and 2 should send a 12v signal to the resistor.
If you're not familiar with electrical diagnose then you'll need to make a guess at which is the defective part. From past experience I would start with the Blower Resistor.

The blower resistor is located left of the blower motor on the rear firewall under the hood. I can send you a picture if I had your email address. I cannot send images through this website.

Note: If you replace the blower resistor and it operates ok but then fails again...something is causing the resistor to fail. Most likely it would be the blower motor. The blower motor can be worn and cause excessive amperage to go through the resistor. In this case you will need to replace the blower motor and the resistor. Does you blower motor sound different than it used to when the car was new? Is it noisier? If yes, I would also replace the blower motor.

Hope this helps you.