Blower motor or blower regulator. They are accessible after removing the wiper system from the engine compartment. The regulator is beneath the motor.

The other thing to look at is the fuse. It often cracks and can work intermittantly but I doubt it would cause a control problem. Anyway the regulator controls the ground side of the blower so to test one must expose the blower wires and jump the ground side.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician