What would cause your blower motor to only run on high in Chevy Express?

A Chevy Express blower motor that only runs on high speed usually points to a problem with the blower motor resistor. This resistor is responsible for regulating the speed of the motor by providing different levels of resistance. When it fails, often the only remaining speed is the highest setting because the full voltage is going directly to the motor, bypassing the resistor.

Other, less likely possibilities include:

* Faulty blower motor switch: While less common than a bad resistor, a problem with the switch itself could prevent lower speeds from being selected.

* Wiring issues: A short, break, or loose connection in the wiring harness between the switch, resistor, and blower motor could disrupt the lower speed circuits.

* Blower motor failure (less likely): While the motor itself can fail, it's more likely to result in complete failure rather than just a high-speed-only issue. However, internal winding issues *could* cause this, but again, resistor failure is far more probable.

In summary: The most probable cause is a bad blower motor resistor. Diagnosing the specific problem would involve testing the resistor, wiring, and switch using a multimeter. If you're not comfortable with automotive electrical work, it's best to take your van to a qualified mechanic.