Central air conditioners are a convenient and economical way to cool down an entire house. Unfortunately, they can be expensive to repair when something goes wrong. If your central air conditioner will not turn on, try to troubleshoot the problem yourself before calling a serviceman out to your home. The problem could be a simple issue like an incorrectly programmed thermostat or a clogged filter.
Check the settings on your thermostat before moving on to troubleshoot the air conditioner unit. Change the batteries in your thermostat if the display screen is blank or flickering. Make sure the thermostat is set to "Cool" mode, the fan switch is in the "Auto" position and the desired temperature is lower than the current room temperature. Move the fan switch to "On" and listen for the sound of the fan turning on. If it turns on, there may be a fault in the thermostat's wiring or it may be miscalibrated.
Check the thermostat's calibration by moving the temperature setting down several degrees and waiting to see if the air conditioner turns on. If it does, the thermostat may be miscalibrated. Recalibrate it according to the instructions in your owner's manual or replace the entire thermostat.
Go outside to the home's circuit breaker box to see if the switch has been tripped or a fuse has blown. Check the fuses and switches for your home's furnace system as well. Some central air conditioners use the furnace fan to move the cooled air throughout the home.
Consult the owner's manual to find out if your central air conditioner has a reset switch. Some models have a switch on the exterior of the unit that must be reset before the system will turn on again.
Replace the air filter if it is dirty. Your central air conditioner may have a shut-off switch that prevents it from turning on if the airflow to the unit is blocked.
Move to the air conditioner unit and look for the two copper lines coming out of the top of the condenser. If the larger copper line feels warm when you touch it, the condenser could be clogged or broken. Call a professional serviceman to replace it.