Check if your thermostat is on the "on" position and make sure it is on the appropriate setting. Ask a friend to stand by the outside condenser and slowly decrease the temperature on the thermostat. One the temperature reading is below the room temperature, you will hear a clicking sound and the air conditioner should come on. If your friend does not hear the air conditioner turning on, the thermostat is not sending a signal. => Turn of the breaker to the air conditioner and remove the cover of the thermostat. The thermostat works on a low energy outlet and hence there should be no worries about being electrocuted. => Expose the wiring in the thermostat and take a picture of it with you phone so as to remember what wire goes where. Loose the screw that are labeled "Rh", "R" and ''W". Remove the wires from underneath and twist them all together. Turn on the breaker for the air conditioner. If you hear the air conditioner turning on, the thermostat needs replacing, and if you don't hear the ac coming on, there is something wrong with the air conditioning system.