The A/C blower only works on med. & high but not low. I changed the switch but wasted $20.00. Still no low speed. What next? a new fan motor or maybe just a resistor?
maybe just a resistor?
That is the classic description of a resistor problem. That is where I would have started.
I agree with Joseph. This is a classic failing resistor pack symptom.
The way the fan is wired, the circuit goes through a stepped resistor setup. On the “low” setting, it goes through the path of highest resistance. The resistance “drops” (uses) voltage, so the fan motor only sees what’s left. It being a DC motor, it goes slow. As you move up the blower speeds, the circuit travels through less and less of the resistor network, leaving more and more voltage for the fan motor. On “high”, the resistor network is bypassed completely and the fan motor sees the full 12VDC and runs at max speed.
As the resistors blow, the lower speeds drop out until only the “high” speeed remains, it being a direct circuit bypassing the resistor network.