Air conditioner problem

[Durhamdp]

I have a 2000 F250 and the air conditioner does not cool unless you are running down the road. When it is in the "Max Air" position the air only blows out the defrost vents. I also have this problem when it is in 4 wheel drive. Looking for help to solve this problem!!

[Drepka]

Vacuum pump no good??? I used to have to "tap" on mine to get it pumping then the ac would come out of the vents I think I also read that this is what is used to engage the autohubs?!

[Durhamdp]

Thanks, I will check that out.