How to fix it: An air conditioner that is running but isn’t cooling is one of the most common problems. Unfortunately, it has a number of potential causes. It could be a dirty air filter, low refrigerant level, or a blocked condensate drain. You can also check for ice around the coils or a dirty outdoor compressor. Or, you may need to add more coolant to your system. Another problem: it may simply be too hot outside to cool your home to your liking. Most air conditioners can only cool to about 20 degrees lower than outside air temperatures.