HVAC Air Flow Switching to Defrost When Accelerating on Dodge Ram 2500

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.

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Average mileage: 162,785 (84,000–275,000)
6 model years affected: 1994, 1995, 1996, 1997, more1998, 1999
13 people reported this problem
3 people shared problem details
1994 Dodge Ram 2500175,000
When accelerating with the vents on it switches to defrost until I quit accelerating.
switches to defrost under acceleration
Air flow switches to defrost when accelerating or pulling up hill. Have not found a fix as of now
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