Your AC shouldn't shut down mid-cycle unexpectedly and then refuse to power back on. There are a few problems that can cause this, and most are easily repaired.
1. Tripped Breaker
The most likely cause is an issue with the circuit breaker. Power surges can lead to a tripped breaker. Simply flipping off the breaker that controls the AC, waiting 30 seconds, and then flipping it back on will often fix the problem. If the breaker continues to trip often, you may need to have the circuit panel checked to make sure there are no issues that are causing repeated power surges.
2. Thermostat Failure
The thermostat is the brain of your system. It sends the signal to power on when temperatures above the set threshold are detected. If the thermostat is malfunctioning, it may not send the signal and the air conditioner will now turn on. If a setting adjustment solves the issue, then the thermostat needs to be recalibrated so it reads temperatures properly. Replacement is necessary if the thermostat fails to work even after adjustment.
3. Bad Wiring
Issues with the wiring anywhere between the AC and circuit breaker or thermostat, or within the air conditioner motor itself, can result in a complete inability to turn on. Sometimes there will be symptoms of a wiring failure, such as the smell of burning metal just before the failure, or scorch marks inside the AC unit. In other instances, you may not be able to spot the damage visually, and the repair tech will have to test all the wiring to determine the location of the short.
4. Frozen Coils
An AC will often shut down completely if the coils become frozen. You can easily spot the cause by looking at the exterior unit for signs of icing up. Coils freeze up when the unit is dirty, the air filter is clogged, or as a result of a refrigerant leak. Your technician can inspect the unit to find which of these issues caused the AC to freeze up, then they will make the necessary repair to prevent it from happening again.
5. Broken Capacitor
The capacitor is responsible for starting up the motor when it is time for a cooling cycle to begin. Ideally, the capacitor has a lifespan similar to that of the entire unit, but occasionally a capacitor may fail prematurely. Your AC tech will perform a capacitor test to determine if it is the cause. If so, you can simply have it replaced.
Contact an AC repair service if you need more help with troubleshooting and repairing your air conditioner, like Vance Air & Heat.