2004 Chevy Impala

My car's air never turns on unless I hit my dash board or a hard bump. When it does turn on it immediately turns off and then I have to hit the dash again. Also, when apply the break it will turn off too. I recently had to have a seal put back on and sealed by the fan that I think produces the air to come through the cabin. I didn't know the seal was bad until I had over 6 inches of water in the passenger side of the car. Is that fan going out? And what is it called?