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Control Head Selector Lever: Bi-Level

Operation is the same as in AUTO position except that conditioned air will be delivered through heater, air conditioning, and defroster outlets (tri-level operation). If maximum heating or cooling is called for, blower will operate at Hi-Blower speed. For maximum cooling, air door will also close off outside air and inside air will be recirculated.

Fig 1: Buick Vacuum Circuit Diagram (Schematic)
G09312001Courtesy of GENERAL MOTORS COMPANY