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HVAC Air Flow Switching to Defrost When Accelerating on Dodge Dakota

Problem Description and Possible Solution

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.

Problem Data
RepairPal Verified
Average mileage: 162,625 (100,000–280,000)
7 model years affected: 1990, 1991, 1992, 1993, more1994, 1997, 1999
22 people reported this problem
Viewing 1 - 8 of 8 comments
During acceleration, the HVAC switches from max cool to defroster mode. Not found source of problem.
Dash vents blow fine normally but under acceleration the unit switches to defroster vent. My mechanic said there is an actuator valve that can get installed somewhere (I think he installed it in engine compartment in the middle of some accessible vacuum line) to at least control the flow vents (floor, dash, defrost) and it does work - but under acceleration, it still blasts thru the defrost vents and when I let off the gas pedal, it always returns to the dash vents. I can live with this but it is annoying.
Same here, AC blows fine at idle, once accelerating, goes to defrost.
still looking for vacuum leak.
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
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.