Check Electrical Panel Check your fuse box for any tripped circuit breakers, this could indicate a bigger problem with your electrical system.
Check Furnace Power Look for the power switch mounted on the side of the furnace. It may also include a liftable metal housing containing a fuse. If the fuse is blackened and burnt, then it will need to be replaced. However, remember that a blown fuse may also indicate a bigger system problem, so the system should be inspected by a licensed electrician.
Check your Thermostat Settings Make sure your thermostat is communicating with your air conditioner and has been set to “cool”. AC will not run if the set temperature and room temperature is same. While that sounds obvious, it’s a small detail that is easily forgotten by a worried homeowner. If you are using a Smart thermostat like NEST, Ecobee or any other, you should check the manufacturers guidelines or contact their technical support. Most of the time there is some software update or a technical issue due to which your smart thermostat is not communicating with the AC.
Check Thermostat Batteries Many programmable thermostats feature a flashing “low battery” icon on their control screen. If you see a “low battery” warning, promptly replace the batteries with new ones.
Check your Furnace Filter If your fan blower is running but it is not blowing as hard as it normally does, then it might mean that the air filter needs to be changed. Furnace Air filters trap dust, hair, and other particles in the air and, over time, the filter gets so full of debris that it can restrict air flowing through your cooling system. On most residential heating and cooling systems, air filters should be changed every 3 months.
Check the Access Door As a safety measure, the Fan blower turns off whenever you open the access door. If it is still open, even slightly, the safety switch inside will prevent operation. Fully close the door and ensure the latch is in place.
Flush out Drain Lines Air conditioner can drain off several gallons of condensate/water a day in summer season. If the drain lines become restricted by sediment or mold growth, the AC will shut down and water will spill out on the floor & inside Furnace. If the drain hose looks dirty, remove the hose, fill it with a mixture of bleach and water (25 percent bleach), then flush it after several minutes.
If you have checked all above things and still your Air conditioner is not working then call a certified technician to look into this.