What could be the problem Actually only blow out of defrost vents no matter which position I turn the knob...

Sorry typo A.C

How do I find out if it manual. or hvac

It's manual. So how do I fix it

Servo motor has cables attached to it to switch the flow of air! In my Toyota the path that the cable took placed too much stress on the servo motor gearing which was made out of plastic! Stripping the teeth from the gear, the motor would rotate to the point where the damaged teeth were located, then the unit would freeze, not allowing my heat go from my feet up to the defroster vents! Have someone turn the knob while you are under the dash look for cable movement. This cable usually directs air flow to the proper vent. I disconnected mine from the motor and moved it manually to the defrost position ( it was winter). If the cable moves freely. Then check the motor that moves the cable! I would recommend finding the pages from the factory service manual. If its vacuum operated then you have a leak in that system. Mine were electrical motors no vacuum lines!

After reading the info above I checked the engine bay on my 2000 Taurus. The larger vacuum lines were all fine. Then I looked at the small ones. On the fire wall in front of the passenger side there were 2 very small vacuum lines connected to a T. One was cracked right were it goes into the rubber end. As I pulled, it broke completely off. I removed the broken piece from the rubber end and reinserted the vacuum line, then plugged it back on the T. My ac went from blowing thru the defroster vents back to blowing out of the dash panel vents immediately! Thanks for the info.

Same problem but never used a sealant! How can it be repaired?? Getting too hot in Texas!!