On ac mode all air flow is dirrected out the defroster. On bilevel mode air flows from defroster, floor and back seat air vent. Never from the dash vents anymore. What causes this and how expensive is it to fix?
Auto Climate controled AC on 1997 Oldsmobile LSS
A loss of vacuum or low vacuum could be the culprit. When all vacuum is lost the climate control defaults to defrost. Check your vacuum line for cracks/loose connections. The line for the climate control runs from the upper intake manifold (rear part) to a tank on the lower front fender and then to the firewall pass thru to the climate control module behind the glovebox.