2005 Express 3500 air cond vent problems

I have a 2005 express 3500 van with front and rear air. The air conditioner works great, but the front will only blow air through the defrost vents. Does this model have vacuum hoses that could be broken, or is it electrical?

Auto or manual air?

Check for good vacuum from engine to heater controls.

Check all plastic and rubber lines and fittings and vacuum ball.
What is the vacuum reading on the lines?