To troubleshoot air conditioner follow the steps below.
1.1 Is the switch in the COOL position?
1.2 Is the temperature setting below room temperature?
1.3 Is there power going to the air conditioner and the furnace.
Note: Thermostats have a delay when switching from heating to cooling or vice versa . This delay can be up to 15 minutes.
2.1.1 Check the emergency shut-off switch for the furnace. The emergency switch should be located near the furnace.
2.1.2 Check the furnace cabinet doors and make sure they are closed properly.
2.2.1 The breakers for the air conditioner and the furnace should be in the “ON” position.
2.2.2 Check the fuse.
3.1 Most air conditioners have a switch/electrical disconnect, mounted outside. Make sure this switch is in ON position.
3.2 Is the fan running on the unit outside?
4.1 If the Plenum (metal that is connected to the furnace) is frozen chances are your filter is dirty and it is causing the evaporator coil to freeze. In this case you should change the filter turn off the AC for 24 hours for the ice to melt.
4.2 Call your local HVAC technician