welcome to the forum! looks like you got a pretty good deal! atleast the interior is easy to clean up!
The defrost only mode could be a broken vacuum line behind the engine starting battery. May also still be a bad EATC vacuum control module. Removing the module and testing the lines with a vacuum pump will diagnose this. The center vacuum line should be draw from the engine and the other lines are the different options for air control. Saw this trick for making a smoke pump to diagnose vacuum hose leaks. Checking for vacuum leaks using home made smoke pump. - YouTube Aquarium air pump or manual air pump for air matress could substitute for the electric pump. If ya find it is the EATC maybe a repair service like this would help. http://circuitboardmedics.com/ford-eatc-electronic-automatic-temperature-control-repair/
Thanks, I searched tapatalks database and clicked on several f150 sites but this one looked like it had more/better info.
