What is wrong if your blower fan motor only works on high speed a 2002 Chevy suburban?

If your 2002 Chevy Suburban blower fan only works on high speed, the most likely culprit is a faulty blower motor resistor. This resistor is responsible for regulating the voltage sent to the motor, allowing for different speeds. When it fails, the motor only receives full voltage, resulting in only high speed operation.

Other less likely possibilities include:

* Faulty blower motor: While less common than a bad resistor, the motor itself could be failing in a way that only allows it to run at full speed.

* Wiring issues: A short or break in the wiring related to the blower motor speed control circuit could cause this problem. This is less likely but should be considered if replacing the resistor doesn't fix the issue.

* Control module problems: The control module that governs the blower motor speed might be malfunctioning. This is less likely, but possible.

In short: Start by replacing the blower motor resistor. It's the cheapest and easiest fix to try first. If that doesn't solve the problem, then you'll need to investigate the wiring and potentially the blower motor itself. A professional mechanic can help diagnose the issue more precisely if you're not comfortable with automotive electrical work.