Cold Air blowing out Top Vent when heat is On
 

I have a 95 XJ w/ 2.5l. Recently i noticed that cold air is coming out the air vent on the dash (only on the driver's side), while the heat is on. The weird thing is that heat is blowing out the floor vents where it is supposed to. It seems like it blows more air right after i get off the highway and stop at a light and then go again. I think it even i feel cold air come out when the heat is not on. (i live in WI and i have the heat on most of the time right now)

I already checked to see if the blend door control valve is getting vacuum and it is, and it seems to be working (i stuck my head underneath and turn the A/C and heat on and watched it move)

What could cause cold air to come out one vent? Vacuum leak? Blend door?

thanks

Kevin

I'm not positive in Cherokee's but I know in other vehicles there is more than on blend door and motor on the system, maybe you are seeing only one move when there is two that need to for defrost?