Ford Van a/c

I have a 1998 Ford club wagon 16 passenger van. The a/c blows very cold air to the rear air unit but has very little coming out in the front. When I turn on the defrost I have nothing. The max a/c blows on the high speed as its supposed to but very little air comes out of the vents. I have put 2 new heating cores in the van. The van has 170,000 miles, its seems since I put in the first heater core I have had the problems, thanks, Paul

If you have a bug shield that sticks up above the front of the hood, it could stop the air from pressurizing your vents while the van is in motion. If not, then the mechanic connected the vacuum lines wrong to the vacuum unit that opens the proper door. He may have left one off too.