Most air conditioning problems give you a hint to help you determine the cause, either by way of noise or odd operating behavior. It can be frustrating when instead of a hint all that happens is the unit won't turn on. Determining the cause may seem like taking shots in the dark. Fortunately, this troubleshooting guide can help you root out the cause.
#1: Check the breaker box
The most common issue is going to be the circuit breaker box. The switch for your AC unit should be clearly labeled. Make sure it is switched to the "ON" position. Sometimes, switches are just a smidge off center, so try flipping it off and then back on. Then, turn the thermostat way down to see if this turns on the AC.
#2: Verify the thermostat setting
If the breaker looks fine, then the thermostat setting is the next place to check. Not only must it be set to a temperature lower than the ambient temperature in the room, it must also on the correct usage setting. For combined HVAC units, make sure the thermostat's been switched over from heat to cool. Also, some thermostats require that you turn on the fan and AC using separate switches, and both must be on for the unit to run.
#3: Try to force cool
Your next step is to try to force the AC to cycle on. Do this by turning the thermostat all the way down. If the AC is receiving power and working, then this will force it to come on. Sometimes when a thermostat is going out it is giving a false temperature reading, which means the AC doesn't pop on because it's reading a cooler temperature than what actually exists. If the AC pops on with the super low temperature, it's time for a new thermostat.
#4: Check for main unit issues
Head outside if you still haven't uncovered the problem. Begin by removing the cover on the AC. Look for anything that could be affecting the operation of the unit. Icy units are a common issue. This causes the AC to freeze up and shut down. Often this is because of a clogged filter so switching it out will fix the problem. Another common occurrence is for something to become lodged in the fan, which causes it to seize. With luck, you can remove it and there will be no lasting damage. Often, the fan may be burned out or broken, which will require a replacement.
If you still aren't sure of the problem, it's time to call an AC repair professional like Cape Fear Air Conditioning & Heating Co., Inc.