How was the refrigerant level checked? Did someone put a set of gauges on and read suction and discharge pressures while the AC was running? (There is no way to know what the charge is in a system without evacuating and re-charging with the correct amount of refrigerant.)
Off hand, I'd guess you are low on freon. Maybe get a can of R134a and a charging hose with a gauge. Available at your local auto parts store. Instructions should come with the kit.
If that doesn't cure it, you should find a pro.
