If the air conditioner switch breaks, then toggling the system among settings like On, Off and Auto does not happen reliably. It is not possible to test whether the air conditioner is receiving power when the switch does not work, making other troubleshooting tasks impossible.
One of the first steps involved in troubleshooting an air conditioner that does not turn on is checking the circuit box, as a blown fuse or tripped circuit is a likely culprit. However, if the fuse has not blown and the circuit has not tripped, another possibility is that one of the air conditioner switches has broken - either the switch on the circuit or the switch that appears on the thermostat. If the air conditioner does not turn on but the circuit has not tripped and the fuse is still in place, checking to see if the switch is working is one of the next steps.
Other possible causes for an air conditioner that does not turn on include a fault in the entire thermostat. If a thermostat runs on battery power, a new battery might fix the problem. The condensation drain may have clogged, leading to a malfunction as well. Dirty or blocked condenser coils can also cause the air conditioner to stop working.