HVAC Air Flow Switching to Defrost When Accelerating on Dodge Ram Van 3500

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: 168,400 (133,000–210,000)
9 model years affected: 1995, 1996, 1997, 1998, more1999, 2000, 2001, 2002, 2003
15 people reported this problem
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problem details
2001 Dodge Ram Van 3500 210,000 mi,
Same symptom on 2001 ram van 2500.
1995 Dodge Ram Van 3500 179,000 mi,
1995 dodge ram 1500 5.9 vent changes to defrost during accelleration