Truck: 1998 F150 supercab V6 5sp.

Problem: When running my AC, as soon as the engine starts to rise in RPM as soon as 1900 rpm the AC stops blowing through the AC vents on the dash and starts to come out the front windshield defroster vents. As soon as I get to cruising speed the AC switch's back to the dash vents . But when there is a small rise in the road and the engine needs to work a little more, the AC switch's to the defroster vents again until the load lightens up to cruising speed .

Any ideas out there guys . Thanks, Mark m

 

Advanced SEARCH keywords "defrost vacuum leak" and my username.

This one needs FAQ status.

Steve

 

When its real hot, and I start my truck and throw the A/C on, it will come out of the floor vents and then come out the dash?