My truck heater fan seems to blow...but comes out VERY slowly at feet ONLY...regardless of electronic switch position. No heat coming out of defrost or front panel. Can hear the fan blow adequately & operates at higher pitch... when changing the fan speed on control panel. Just no heat at defrost or main front panel. Is this system vacumme operated or what are the possible things and locations to check for failures of this sort? THANKS!!!

As simple as it sounds look for debris around the fan intake. I had a similar problem with low flow and had a plastic bag around it. Also does your fan sound like the bearing is bad? if none of those you can take off the heater case to the left of the fan which stores your heater core, if you look up past your core with a flash light you should see a door that actuates with the heater switch I believe that door is vaccum actuated. I'm not sure if this will cure it but probing may allow you to see somethign you haden't seen before

Thanks A Lot For Your Time And Advice !!!