Why does the heater fan only run on high speed in 02 trailblazer?

If the heater fan in a 2002 Trailblazer only runs on high speed, it is likely due to a faulty blower motor resistor. This component controls the fan speed, and when it fails, it often defaults to the highest setting. Additionally, a short circuit or wiring issue could also contribute to this problem. Checking the resistor and associated wiring is recommended to diagnose and fix the issue.