If your HVAC is running but not cooling, the first thing to do is go and check the thermostat. Just make sure it is set to cool. Then check the temperature settings as someone might have changed it by mistake. If it is set to off, switch it to heat and then back to cool. Wait a few minutes, and you will hear the AC unit kicking in. Check if it starts to blow out cold air or not. If yes, problem solved. If not, you can check one other thing before calling in an expert.