If the cool air has stopped flowing, the first thing you should do is check your thermostat. Here are the steps you should take: If your thermostat display is blank, change the batteries. If the display is still blank, remove the thermostat from the wall and check the wires to make sure it’s getting power. Use a multimeter to check the voltage. If you’re not getting voltage, check your fuse box to see if any fuses have been blown or tripped. If the fuses look good, locate the switch connected to your central A/C and switch it on and off to reset the connection. If it’s getting power, but the screen is still blank, go outside and check the condenser to see if a fuse has been tripped. If your thermostat still isn’t working, it may be time to replace it. Check the warranty to see if it’s expired. If your thermostat is working, but the air conditioner won’t turn on, you should also: Turn on the fan to see if the blower is getting power. Change your air filter if it’s more than one month old. The buildup of dirt and debris could be preventing air flow. Check the condensation drain. If you’re still experiencing problems, call an HVAC professional.