You say quit and then start working. Did it start working after the car was cycled off and on? If it did it was something in the belt protection system. If it came and went while the car stayed running I would suspect a problem with the Mode door potentiometer. Lots have been writen on both areas.

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