Turn off the air conditioner
Unplug it from the power source or switch off the circuit breaker
Wait 5 to 10 minutes
Plug it back in or turn the breaker back on
Press the reset button if your unit has one
Use the remote control to restart the unit
Check the thermostat settings
Confirm the air filter is clean
Inspect the breaker and fuse if the unit still does not start
Contact a qualified technician if the problem continues