For whole home units (like central air), double check to make sure your thermostat settings aren’t the problem. Make sure the unit is on, the desired temperature is lower than the current temperature, and that the unit is set to cool instead of heat.
For portable or window units, check that the settings on the unit are correct. If they are, try restarting the unit and checking to make sure there is power flowing to the outlet that it is plugged in to.
If the above steps don’t work, give us a call and we will come take a look.