Merth

I have a 2002 F-150 supercrew and recently the AC has started automatically switching vents. Example will be in automatic mode and blowing out the dash then switch to defrost vents. Sometimes it may switch back after a bit but most of the time I have to select vent then automatic to get it back to the dash. Many times it will do no good as after a few mintues it will do the same thing. Also I do have the electronic temp and select. Could this be a vacuum issue? Any suggestions as to how I can diagnois this would be great. Thank you

ymeski56

I think the vent door shutters are modulated by vacum. Look for aloose connect or cracks in the small semi-rigid plastic vac lines under the hood, passenger side firewall. I think there's a vac moter also.

torkum

Check for a crack or break in the vacuum line going into the firewall behind the battery.