HVAC Air Flow Switching to Defrost When Accelerating on Dodge Dakota

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.

RepairPal Verified
Average mileage: 157,142 (100,000–280,000)
7 model years affected: 1990, 1991, 1992, 1993, more1994, 1997, 1999
18 people reported this problem
6 people shared problem details
During acceleration, the HVAC switches from max cool to defroster mode. Not found source of problem.
still looking for vacuum leak.
1999 Dodge Dakota120,000
No solution yet. Switches to defrost vents under acceleration. Suspected vacuum issue.
Same here,no vaccuum leaks and all the check valves under the hood check fine.
air flow switches from bilevel to defrost when accelerating
1990 Dodge Dakota148,000
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.
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