Lumina overheats at high speed+a/c problem

was wondering if anyone knows what could be the problem with my Lumina. After I drive it on a highway for about 30 minutes it overheats badly. at the same time my air conditioning disappears, but if it ever comes back then the car is not overheated anymore !! however i still have a/c comming out from underneath, but nothing from the dash panel.
If anyone has any ideas, please let me know.
thanx.

it sounds like you have a blocked radiator. It is also possible that debris has gotten between the radiator and a/c condenser and is blocking air flow.