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: 129,480 (50,000–272,000)
9 model years affected: 1995, 1996, 1997, 1998, more1999, 2000, 2001, 2002, 2003
106 people reported this problem
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Viewing 1 - 20 of 48 problem details
1997 Dodge Ram Van 1500 200,000 mi,
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.
1999 Dodge Ram Van 1500 135,765 mi,
my problem is that it stays on defrost wont change to heat or vents. does antbody have a solution
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.
1997 Dodge Ram Van 1500 174,000 mi,
heater/ac only works on defrost
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
1999 Dodge Ram Van 1500 125,000 mi,
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.
1998 Dodge Ram Van 1500 170,000 mi,
ac and heat only comes out on defrost.
2001 Dodge Ram Van 1500 135,000 mi,
a/c switches to defrost on acceleration or moderate incline
1996 Dodge Ram Van 1500 160,000 mi,
I have the same problem on my 97 3.9L B1500 I installed two check valves this did the trick
AC/heater awitches to defrost when acceralating
1999 Dodge Ram Van 1500 145,315 mi,
Air switches from vent to defrost while acceleration or under a load and returns to vents when I let off the throttle
2002 Dodge Ram Van 1500 64,000 mi,
when accelerating the AC/Heat moves from the front vents to defroster vents and when I let off the flow returns to the front
1999 Dodge Ram Van 1500 165,000 mi,
Hey.....I feel your pain! I went nuts trying to find the vacuum leak, and followed the lines to a little rubber stopper thing at the center of the firewall. It has holes in it and I noticed one was hanging loose......I had to trim some off the ends of the tubing, and then stuck it back in firmly, and whaddya know? AC was blowing out the vents again!!! No more defrosted ac. Hope this helps. Tennessee Jed.
2000 Dodge Ram Van 1500 70,000 mi,
Heat or ac redirects to defrost when accelerating.
1999 Dodge Ram Van 1500 54,661 mi,
When I accelerate the ac switches from dash to defrost.
1998 Dodge Ram Van 1500 70,000 mi,
Ac changes to defrost when stepping on the gas
2000 Dodge Ram Van 1500 198,000 mi,
Air conditioning system cuts off go off when turns on goes to hetter
Upon acceleration the vent selection changes to defrost.
Defrost blows air but does not defrost windows
1998 Dodge Ram Van 1500 112,000 mi,
Switches to defrost on acceleration and noq finally wont switch back