ForTwo Air Conditioning Problem

Hello, I bought a ForTwo BJ 2004 from a Hämdöer (in September 2007). Now I switched on the air conditioner for the first time, since I never needed it before. The engine speed drops short, I think, a sign that the compressor has plugged in via the magnetic coupling. The air, which then comes out of the nozzles (of course turned on) is both at stage 1 and at stage 2 minimally cooler than the internal air (at the external temperature approx. 23 °C). You can’t talk about cold air at all. Is it normal that the greenhouse gas has already erupted after about 4 years? Does anyone have any idea what a refill costs? Do you have to do this at the smart center, or can you do it at a free workshop? Thanks Rambaldi