How To Troubleshoot Heating Or Cooling Problem.

Check to make sure that your control or thermostat is set in cooling mode. Make sure that the temperature is set cooler than the current indoor temperature. If it isn’t, your system won’t know to provide cooling.
Make sure your outdoor cooling (condensing) unit is running. If not, check the circuit breakers in your home’s circuit breaker box (or electrical panel). They should be in the ON position.
Check the main power switch for your outdoor unit, usually found within a few feet of the unit in a box mounted to the exterior of the house. Make sure it’s in the ON position.
Ensure that the blower motor in your furnace or air handler (fan coil) is running. If the system is set for cooling, the blower motor should be running. If not, check to make sure your indoor unit switch is in the ON position.

Check the filter for buildup. If you have one-inch-thick furnace filters, a once-a-month change is recommended. Two-inch-thick filters—and other high-capacity pleated filters—usually only need to be changed every other month, depending on the type. If you don’t change it, the filter will eventually become so full, it will block the proper airflow and cause your outdoor air conditioner unit to shut down.
Check all return air grilles to make sure they are not blocked. Return air grilles are larger and are located on a wall or the ceiling in newer homes. Older homes frequently have return air grilles on the floor.
Check all supply registers to make sure they are open and blowing air.

Your system is struggling to keep up and seems to be turning itself on and off frequently.
Your indoor summer humidity levels seem unusually high.
You hear your indoor-unit fan coming on but the air from the registers isn’t cool or the fan is turning on and off more frequently than usual.

How to troubleshoot your way out of a heating or cooling problem.