My AC is broken and only works when the technician comes

My AC keeps blowing out hot air. it only happens in late afternoon and it is unpredictable. sometimes for a 10 minute period it shoots out cold air, then for another 40min it's shooting hot air.

When I call apartment maintenance, the maintenance guy comes and the AC works fine. an hour later, it's 85 degrees in my room.

I don't know what to do. i hate this. i just moved in last week.