1. Remove the climate control unit.
2. Inspect for continuity between the fan switch terminals using an ohmmeter.


Climate control unit inspection
Defroster switch inspectionMazda 6 Service Manual: Instrument cluster removal/installation
Caution
When replacing the instrument cluster, the configuration procedure must be
performed before removing the instrument cluster. If the configuration procedure
is not performed before removing the instrument cluster, it is possible that the
instrument cluster will not operate normally. ...
Mazda 6 Service Manual: Driving Tips
WARNING
Do not let the vehicle move in a direction opposite to the direction selected
by the selector lever: Do not let the vehicle move backward with the selector
lever in a forward position, or do not let the vehicle move forward with the selector
lever in the reverse position. Otherwise, t ...