I’m considering buying a 2001 F250 (diesel) but when I test drove it, noticed that the climate control selector does not work, it only blows from the defroster regardless of the position of the knob. Some quick research indicates that there is a vacuum problem - possibly bad vacuum pump. Any idea how much it would cost to replace so I can negotiate the price accordingly? By the way, I also couldn’t get the AC to blow cold air - only hot (not ambient, but hot).
You may not need a pump.
It is possible the blend door (vacuumed controlled) has disconnected from the control linkage or there is a vacuum hose leak.
The A/C may just need recharging, IF the seals aren’t dried up.
The Ford vacuum pump is # 6C3Z-2A451-A . list price shows $ 200.91 but generaly wholesales at $ 150.00. Not sure about aftermarket sources but the diesel engine is made by Navistar ( FKA international harvester ) and might be available there too.