Many people think that the cause of their air conditioner not blowing cold air is because the filter is dirty. However, a dirty filter can create a build-up of dust and grit, impeding the flow of cool air through the unit. This can cause the air conditioner to run hotter and make it more difficult for your room to cool down. 5 common causes of AC not blowing cold air Thermostat setting incorrectly If the thermostat is set incorrectly, your AC might not be blowing cold air. Here are some of the common causes: -The thermostat is not properly calibrated. This can be caused by a wiring mistake or by incorrect installation instructions. If you have a newer home, you may also need to replace the thermostat if it has not been working correctly for a while. -The thermostat is stuck in low mode. In this case, your AC won't go on or will be very weak. You can fix this by pushing the button on top of the thermostat more often or changing the setting to high mode. -The fan isn't working p