Air problem

The other day while driving my air would stop blowing out the vents any time any load was put on the engine. I figured the WOT sensor went. But this morning I found out that It did not stop blowing completly it woud blow out the defroster holes on the dash and when I would let off the gas it would return to the vents. Strange to me at least can anyone offer any direction on were to start looking

I am not absolutely sure about this but here goes. There should be vacuum lines that run to the controls for your a/c. And I'm pretty sure it's vacuum that is behind the button pushing we do to change from say heat to defrost and so on. If there is a vacuum problem going to the console, and it could be from anywhere on the engine, this would cause the problem you refer to. You might try buying a cheap vacuum gauge. Get a reading from one of your lines and start pinching them off to see if the vacuum increases. The gauge will go from 0 in hg to 30 in hg. You are looking for the reading to increase from say 15 in.hg. to 20 when you pinch one of the lines. In other words the dial will increase counter clockwise. Pay no attention to the numbers I listed. The important thing is that you see an increase in negative pressure. I bought a cheap one from advance auto for 17.95. It also does gas pressure. Good luck.