HVAC Air Flow Switching to Defrost When Accelerating on Dodge Ram Van 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: 128,519 (50,000–272,000)
9 model years affected: 1995, 1996, 1997, 1998, more1999, 2000, 2001, 2002, 2003
93 people reported this problem
40 people shared problem details
A/C blows normal until you accelerate then it moves to the defrost vents then the feet vents. when I lift off the gas it imediatly returns to normal.
47 people like thisFlag inappropiate
my problem is that it stays on defrost wont change to heat or vents. does antbody have a solution
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We travel on the highway as we increase speed the ac/heater switches over to defrost ....we release the gas pedal it switches back to normal any solutions.
22 people like thisFlag inappropiate
heater/ac only works on defrost
19 people like thisFlag inappropiate
ac and heat only comes out on defrost.
10 people like thisFlag inappropiate
a/c switches to defrost on acceleration or moderate incline
9 people like thisFlag inappropiate
A/C blows normal until you accelerate then it moves to the defrost vents then the feet vents. when I lift off the gas it immediately returns to the floor.
8 people like thisFlag inappropiate
I have a 1996 dodge ram 1500 with 3.9. when I accelerate the ac/heater switches from vent to defrost, I dont know how to fix or check for problems
8 people like thisFlag inappropiate
I have the same problem on my 97 3.9L B1500 I installed two check valves this did the trick
5 people like thisFlag inappropiate
AC/heater awitches to defrost when acceralating
5 people like thisFlag inappropiate
Ac changes to defrost when stepping on the gas
Heat or ac redirects to defrost when accelerating.
the blower will switch from floor to defrost upon acceleration and back when coasting
Not fixed yet
When the van is accelerating the AC will turn redirect to somewhere else, maybe the defrost vents, and when I let off the gas the AC comes back
switch for the air fan speed has when out two times you have to buy the hole switch control temp/fan speed/turn heat and air on / and mirrow defrose
Hoping to find out what to check to make the dash vent operate again... Thanks!
When accelerating, especially when accelerating uphill, the air flow switches from my front dash vents to my defroster vents. The problem is a vacuum leak, I just don't know where. I have seen reports from other vehicles that the vacuum leak would be in the vacuum line to the exhaust manifold; specifically the valve there is either dirty or damaged and can't hold any pressure.
accelerate lose air cond
Air come out thru the vents ,at soon i step on the gas pedal it switches ,to defrost by itself ,i let go the gas pedal and it switches to the floor
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