A/C works, blows thru defroster and lower but not bi-level

The a/c mode doors on your 1997 Oldsmobile Regency use engine vacuum to operate. The vacuum source in under the hood. You should find a squarish black plastic tank mounted on the center of the firewall under the hood. Make sure the vacuum hoses are properly connected and you have the proper vacuum supply from the engine. Also check for proper operation of the check valve in the vacuum supply line from the engine.