There are many reasons why an AC might fail to cool properly. AC units have several different parts that can malfunction or break, which is why it’s important to check the owner’s manual before making any attempt at AC repair. If the air conditioner isn’t cooling properly, make sure all exterior vents are open and free of obstructions, and check for a dirty AC filter. Look inside the AC unit itself for clogs or damage – AC coils should be unclogged and AC condensate drain line free of AC debris.