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

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: 162,666 (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 comments
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
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
HVAC Air Flow Switching to Defrost When Accelerating
Not getting air through vents vacuum line disconnected dont know how to hook back up
HVAC Air Flow Switching to Defrost When Accelerating
Don't now how to fix, need help
hvac air flow switching to defrost whe accelerating
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.
Now at 187000 I am having trouble with no heat. The heater core feels hot under the dash but blows warm air.