The AC/heater (HVAC) system may unexpectedly switch to the defrost mode when accelerating. This system is operated by engine vacuum and should be inspected for any vacuum leaks if this problem develops. There is also a revised vacuum check valve available to address this concern.Google+
Car Problem Reports
Dodge Dakota HVAC Air Flow Switching to Defrost When Accelerating
Dodge Dakota Problem
Average Mileage: 182,666 mi (120,000 mi - 280,000 mi)
Visitor, 1999 Dodge Dakota, 120,000 mi
No solution yet. Switches to defrost vents under acceleration. Suspected vacuum issue.
Visitor, 1990 Dodge Dakota
Same here,no vaccuum leaks and all the check valves under the hood check fine.
Visitor, 1992 Dodge Dakota
air flow switches from bilevel to defrost when accelerating
Visitor, 1990 Dodge Dakota, 148,000 mi
Air flow in vehicle keeps cycling and flips some sort of gate in the heater duct system.....plus in driving gear timing seems horrible...In park or nuetral it sounds decent but still using an incredible amount of gas.