MY AIR DOES NOT WORK?

What is your question?

WHEN I TURN MY AC/HEATER NOTHING HAPPENS I MEAN IT WILL ONLY BLOW COLD OR HOT WHEN IM DRIVING 45MPH OR FASTER. I WAS TOLD IT HAS SOMETHING TO DO WITH SOME PART BEHIND THE GLOVE BOX??????WHAT IS DAT CALLED AND IS IT EASY TO REPAIR I STAY IN FLORIDA AND NEED AC........