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
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.
Air flow in vehicle keeps cycling and flips some sort of gate in the heater duct in driving gear timing seems horrible...In park or nuetral it sounds decent but still using an incredible amount of gas.