Check your thermostat first if your HVAC system is running but not cooling. Make sure it is set to “cool”. If it is, look at the temperature setting to see if it has been changed.
If your air conditioner isn't cooling even when it's turned on, you may have a clogged or obstructed coil. Unfortunately, a broad range of contaminants, including grass, mud and other impurities, can make their way into this equipment. This can cause a major blockage, which can cause the system to fail.
A refrigerant leak is another possibility. Refrigerant is required for your air conditioner to function correctly. A refrigerant leak can cause poor system reliability and perhaps cause the unit to shut down completely.