Turn the ignition key to the ON position
Set the blower switch to each speed setting
Check whether the blower operates on some speeds but not others
Locate the blower motor resistor
Disconnect the electrical connector from the resistor
Inspect the resistor and connector for heat damage, corrosion, or melted terminals
Set a multimeter to measure resistance
Measure resistance across the resistor terminals
Compare the readings to the vehicle service specifications
Check for open circuits on any resistor path
Check for continuity through each resistor coil or circuit
Verify battery voltage is present at the resistor connector with the blower switch on
Verify the blower motor receives output voltage from the resistor on each speed setting
If equipped, test the thermal fuse for continuity
Replace the resistor if any circuit is open, out of spec, or visibly damaged