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.
HVAC Air Flow Switching to Defrost When Accelerating on Dodge Ram Van 1500
Average mileage: 127,656 (50,000–272,000)
102 people reported this problem
46 people shared problem details
1997 Dodge Ram Van 1500200,000Visitor
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 1500135,765Visitor
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 1500174,000Visitor
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 1500125,000Visitor
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 1500170,000Visitor
ac and heat only comes out on defrost.
2001 Dodge Ram Van 1500135,000Visitor
a/c switches to defrost on acceleration or moderate incline
1996 Dodge Ram Van 1500160,000Visitor
I have the same problem on my 97 3.9L B1500 I installed two check valves this did the trick
1998 Dodge Ram Van 150070,000Visitor
Ac changes to defrost when stepping on the gas
1999 Dodge Ram Van 1500145,315Visitor
Air switches from vent to defrost while acceleration or under a load and returns to vents when I let off the throttle
1999 Dodge Ram Van 1500Visitor
Defrost blows air but does not defrost windows
2002 Dodge Ram Van 150064,000Visitor
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 150054,661Visitor
When I accelerate the ac switches from dash to defrost.
1999 Dodge Ram Van 1500165,000Visitor
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.
1998 Dodge Ram Van 1500112,000Visitor
Switches to defrost on acceleration and noq finally wont switch back
2000 Dodge Ram Van 150070,000Visitor
Heat or ac redirects to defrost when accelerating.
1995 Dodge Ram Van 1500158,000Visitor
the blower will switch from floor to defrost upon acceleration and back when coasting
2001 Dodge Ram Van 1500150,000Visitor
Not fixed yet
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