HVAC Air Flow Switching to Defrost When Accelerating on Dodge Ram 1500

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: 163,153 (60,000–253,000)
8 model years affected: 1994, 1995, 1996, 1997, more1998, 1999, 2000, 2001
36 people reported this problem
8 people shared problem details
When accelerating with the AC on, the air goes from the vents into the defroster vents. I saw that you had a solution, yet it's too vague for me. Could you tell me about this revised check valve? Does it have a component name, or a part number so I can get one and get my truck fixed? Will I be able to purchase it myself? More info please. Thank you
1997 Dodge Ram 1500141,000
havac switch to defrost when on a/c on acceleration have looked in engine compartment dont see any broken lines have any were to look
1997 Dodge Ram 1500195,000
HVAC Air Flow Switching to Defrost When Accelerating
1995 Dodge Ram 1500187,000
Not getting air through vents vacuum line disconnected dont know how to hook back up
1999 Dodge Ram 1500115,000
HVAC Air Flow Switching to Defrost When Accelerating
1999 Dodge Ram 1500160,000
Don't now how to fix, need help
1998 Dodge Ram 1500156,000
Now at 187000 I am having trouble with no heat. The heater core feels hot under the dash but blows warm air.
hvac air flow switching to defrost whe accelerating
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