HVAC vents not changing

hey guys. went to use my A/C last night when i noticed the MAX A/c wasnt working. It would blow cold air, but it would not go into recirculate mode. Then after that i noticed air just came out of the front vents and floor only, no matter what position the switch was in (floor, vent, defrost) The switch still makes the a/c compressor kick on when its switched to max a/c or defrost, but the vent position doesnt change. I checked all vacuum hoses under the hood and everything looks fine, (although i couldnt find one specifically that goes right into the HVAC unit) I paid special attention to the areas around the spark plugs and wires i recently changed, but couldnt find anything suspicious.

Any suggestions on where to start? Also, can anyone tell me where under my hood i would find the vacuum line that goes to the HVAC

NEVERMIND. Just found the vacuum line i was asking about. apparently it runs near the battery, where corrosion from the battery can fall/drip on to the line and cause it to corrode/melt.

Good find, I had the exact same problem and traced it to my battery area.