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.

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Average mileage: 162,666 (60,000–253,000)
8 model years affected: 1994, 1995, 1996, 1997, more1998, 1999, 2000, 2001
38 people reported this problem
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Viewing 1 - 9 of 9 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 1500 141,000 mi,
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 1500 195,000 mi,
HVAC Air Flow Switching to Defrost When Accelerating
1995 Dodge Ram 1500 187,000 mi,
Not getting air through vents vacuum line disconnected dont know how to hook back up
1999 Dodge Ram 1500 115,000 mi,
HVAC Air Flow Switching to Defrost When Accelerating
1999 Dodge Ram 1500 160,000 mi,
Don't now how to fix, need help
hvac air flow switching to defrost whe accelerating
2001 Dodge Ram 1500 150,000 mi,
HVAC switch to defrost when on a/c on acceleration. Apparently there were spacers that needed to be replaced in the vent system. It seems to have fixed the problem.... for now.
1998 Dodge Ram 1500 156,000 mi,
Now at 187000 I am having trouble with no heat. The heater core feels hot under the dash but blows warm air.