Air conditioning only at high speed :/

Hello So now my moose is also on :/ I noticed the following problem already last summer, then I used the KD, read out and had the cooling liquid filled up (has not missed much), then wurds anyway colder again and I used the climate anyway. Today on one of the first warm days with climate needs the problem occurs again And that is when I start the engine, climate turns on this runs about 5 min. impeccable, then it gets warm. 3 possibilities: -AC again from 10min. wait, then you go again for 5min. -driving at high speed 5000-6000 -Open window -sweat Volvo V50 2.4 EZ 2004 what can that be?!