An air conditioner's compressor controls the distribution of cold air throughout the house. When the compressor is not coming on, your air conditioner unit will not run properly. There are a lot of factors that determine whether your compressor will turn on, including blockages and problems with the thermostat that may prevent the compressor from working properly. Proper troubleshooting will help you isolate the problem and prevent expensive, unnecessary repairs. Often, a little cleaning is all your unit needs.
Check the power to the unit on the inside and outside of the home. Plug in the power cord for the condenser unit on the outside of the home and inspect it for any damage. Inspect the fuse box for the unit and check for any flipped switches. Remove any broken fuses and replace them.
Turn down the thermostat in the house. The condenser will not turn on if the air inside the house is cooler than the thermostat is set to.
Open up the thermostat and inspect the wires. Pull out the connectors and inspect the wires for any corrosion. Set your multimeter, a unit used to measure electrical current, to the "X1" setting. Touch the probes of the multimeter to the thermostat connectors. It should read zero or infinity. If you get any other reading, you may need to replace the thermostat.
Check the ducts coming from the central unit for any blockages and remove them as necessary.
Remove the filters from the unit and replace them if they are dirty.
Remove all grass from around the outside condenser unit to prevent blockages.
Unplug the condenser and vacuum the fins with a vacuum fitted with a soft brush attachment.
Remove the screw from the top of the condenser unit and remove the top. Spray the inside of the unit with a hose to remove any debris.
Call a service professional to have your unit inspected if it still doesn't work after you've completed these troubleshooting measures.