Cab A/C blower switch stuck on high

[Wmjp]

Hello everyone, I recently had the a/c blower motor fail on my e450. Simple to replace and not too expensive. After I installed the new unit my ac will only work in the high position ie. No speed control. I did some troubleshooting and the switch is functioning properly. I assume that there’s another component that has failed. Any suggestions would be helpful. Thanks 🙏

[avfordguy]

Resistor pac is blown, any auto parts stores have them, common ford part, it is located near where you replaced the blower motor, has a white connector and about 4 or 5 wires.

[Wmjp]

Thanks avford. You were spot on. Easy repair.

[avfordguy]

Cool, glad I could help !
Happy travels ( with cool air)

[CharlesinGA]

To elaborate somewhat. The blower resistor probably has a thermal fuse on it. If it gets too hot, it blows, and the resistor no longer functions. High blower does not use the resistors so it is the only position that works. The reason the thermal fuse blew was either your blower motor is drawing too much amperage (meaning it is failing) or that you frequently have it on the lowest speed then turn the vehicle off, and when you restart it with the blower on lowest speed, it gets way too hot and blows the thermal fuse. This happens because the resistor pack depends on air from the blower to cool it, and during the start it sees lower voltage, thus higher amperage and the resistors, are all in series in the low speed position so the most heat is being generated, conbined with the blower not really flowing any air to speak of.

Always turn off the blower when you shut the vehicle down.

I had this happen twice on a '99 Plymouth Breeze, it was annoying to spend $20 to buy a new resistor every time, and I finally figured out which coil of the resistors was the one for low speed (along with all the others) and cut out that coil, then the blower worked on 2, 3, 4 but not 1.

Charles