Hey guys, so heres a little back story, my dad has a 2003 f350 6.8l and last year after the winter months my dad had switched his ac/heater control from defrost to ac and it took like 10-20 seconds for it to switch and his ac only worked on max ac. Fast forward some and again after being on defrost through the winter it wont switch off of defrost at all now. Fan speed works but when you move the selector it doesnt change the direction of airflow. Any suggestions on where to start? Thanks for any advice or help

Ha so it is vacuum controlled. My dad was like theres no way its vacuum controlled lol

Thank you for the info! Now to just track it down, i wonder if it may be the reservoir because there is no vacuum going to the front hubs when you engage the 4wd. I will deff see if we can trace the vacuum lines

Thanks project i appreciate the help!