A/C Mode changing during acceleration

[xJohnnyOx]

Well, as i get closer to 300K Miles, more interesting issues are popping up.

This new one is a bit of an annoyance, but may also be affecting engine performance if it is due to a vacuum leak letting in unmeasured air.

While in Max A/C mode, when accelerating or climbing a hill, the A/C mode changes from panel vents to front window (like it is going into defrost mode, but the cool air is coming out the dash front window vent). I started looking for a vacuum leak (and found a small one and fixed it), but issue still exists.

Anyone else have an issue like this?

xJohnnyOx

 

[99WhiteC5Coupe]

Well, as i get closer to 300K Miles, more interesting issues are popping up.

This new one is a bit of an annoyance, but may also be affecting engine performance if it is due to a vacuum leak letting in unmeasured air.

While in Max A/C mode, when accelerating or climbing a hill, the A/C mode changes from panel vents to front window (like it is going into defrost mode, but the cool air is coming out the dash front window vent). I started looking for a vacuum leak (and found a small one and fixed it), but issue still exists.

Anyone else have an issue like this?

xJohnnyOx

From your engine vacuum source, follow the vacuum lines(s) and see if there is an inline vacuum check valve which may be malfunctioning?

 

[Splicer1998]

I started looking for a vacuum leak (and found a small one and fixed it), but issue still exists.

Anyone else have an issue like this?

xJohnnyOx

Yeah, vacuum leak for sure. Very common problem on these.
Best bet is to head on over to the FTE (Ford Truck Enthusiasts) site for troubleshooting tips, this place is a ghost town.
Or, if you're feeling lazy, just use the rear air and point the ceiling vents towards the front

 

[homersson99]

I also have this issue with my 99. I found and fixed one leak which worked for half a ride into town when it happened again. My plan is to hook a smoke machine to the lines in short order. But until then, I too am prescribing to the rear vents cooling my neck for now!