Hello to everyone:
I have had vacuum problems for some time now and have never been able to resolve them. I have a 2.5 I4 and when I put the a/c blower on MAX, the air stops blowing through the regular vents and blows out the defroster vents.. It does it most when going up a hill. While working on the truck over the weekend, I found a gray vacuum line that started under the blower motor and ran over to the passenger rear of the motor. It just stopped at the rear of the engine and I could never find where it could connect. This was one of the small gray plastic lines, not a rubber line. Any help would be greatly appreciated. Thanks, Skip

 

It goes to your heater control valve. The 4 port valve on your heater core lines. That is your problem because when MAX A/C is selected the heater core valve closes, if this line is open then the whole "circuit" will lose vacuum. This includes the front vents and the recirc door.

 

Thanks Sheltonfilms
I replaced the line and cannot believe how much better the truck runs.

Thanks again, Skip