I think he means the recirculation fan button that you push that keeps the blower fan blowing while the car is off. Its useful for winter if you're making a short stop somewhere or getting gas as it keeps blowing residual heat into the cabin.

OP I think your hvac controls might be going bad. Ive had it happen to me once and it would cause erratic blower speed. I bought a used one off ebay and swap it and my problem was fixed.