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This can either be caused by a broken floor/defrost door or mode door in the heater box. It's most likely the floor/defrost but could be either one, sometimes both doors are found to be broken. To know for sure which door is broken a calibration test can be done with a scan tool, but the damage will be apparent with a visual inspection of the doors when the heater box is disassembled.
HOW THESE DOORS OPERATE BY ELECTRIC MOTOR ?
AND WATH ABOUTH THE PANNEL MODE ?
WERE I START TO LOOK AND WHAT I HAVE TO DISASSEMBLE TO START MY VERIFICATION ??
Yes, all doors are controlled by electric actuators. The control head on the dash controls the actuators to move the doors.
To find and repair the broken door(s) the heater box has to be removed and disassembled after the dash is rolled back for access to the heater box.