"The first thing that you need to keep in mind while you experiment the DIY methods in your central air conditioner is to turn off the power in the first place. You need to make sure that the problem is not with the furnace. You will have to set your thermostat to A/C mode and lower the temperature setting. If you see that the furnace fan kicks in, then you can be sure of the fact that the problem is not with the furnace. In case the furnace do not run, then, you can try resetting the furnace circuit breaker. Even after these steps, the system still does not run, you need to call in an HVAC expert. The next thing that you could do is to check the condenser. In case the condenser of your system is not running you could check for blown fuses or tripped circuit breakers at main entrance panel or at separate entrance panel and accordingly restore the circuit. You could also try lowering the thermostat. When all these tricks fail, getting in touch with a professional is recommended. The other important things that you can try out before calling in a professional is cleaning the evaporator and the filter. "