My son in law's 96 lincoln t/c has no hot air comming out vents. It looks like the vacumm controls work when you go full cold to full hot(it is all digital control) and the engine is warm. I noticed a sensor to the right of heater/a/c controls but not sure how to check it. We live in nebraska so heat is a must, it blew good cold air in summer. Could you give us a suggestion on where to start?

Ok let's start at beginning. with engine running at operating temperature[at least 90 to 120 degrees] or if you don't have a digital engine temperature sensor, at least mid range, be careful and remove radiator cap, add anti-freeze until you see it flowing in the radiator,side to side or any motion also good. if it blows and blows out of the radiator extremely, you have another problem. wish i were there just to help. but you gotta do what you can. is there any fluid or a sweet smell inside the car or a leak under the dash onto the passenger side floorboard? if not, thats a really good thing! no bad heater core leaking into the car. make sure the radiators full!! with engine running, no explosive bubbling from the radiator? great. if so, bad. heater core bad or a bad radiator. thermostat been replaced anytime? in last year or so? maybe that bad. with engine OFF. NOT RUNNING,hood up,grab the engine fan, try to move up and down, fan only ok? if the fan has up and down play, any at all, water pump. leaks from under the car? at center of underneath the engine fan? look for a bad water pump. i know nebraska,brother lived there and alaska also. eeh? wish you the best and hope this helps you greatly! thank you for choosing fixya.com