Dirt and grime on AC condenser coils make it harder for your equipment to transfer heat. This means that it will have to run longer and work harder in order to do its job. By doing this, you will force the machine to use more energy and cause some of its parts to have damages as well as possibly break down.
Dirty coils can also become corroded. If this happens you could be dealing with refrigerant leaks which is not good. There are several ways that your coils can become dirty. An example is if your outdoor unit is located near a street, it can become exposed to exhaust. This will lead to a build-up on your coils. Also, natural debris such as dirt and foliage can also build up on your ac condenser coil, which can cause issues. When it comes to the indoor coils, pet hair and dust can build up, especially if your air filter is dirty.