If you examine either the exterior or interior portion of your AC, you will likely notice a series of vents or "fins." These fins are an important part of your air conditioner, without which it won't properly cool your home. The following can help you understand both their purpose and how to maintain them so you can avoid expensive repairs.
The fins on the exterior unit are called the compressor fins. These fins move heat away from the unit, thus allowing the main exterior unit to stay cool so it doesn't overheat. This also moves away from the heat as it is removed from the incoming air, thus allowing it to cool your home. Interior unit fins are called evaporator coils. These fins complete the thermal heat exchange process that removes heat from the incoming air so only cool air is blown throughout the home. The air is blown across these fins so that an evaporative process can cool the air sufficiently.
There are also two ways that fins can become damaged. The most common damage is dirt, which can affect both compressor and evaporator fins but is more common on the exterior fins. When the fins become encrusted with dirt, dust, pollen, or other debris they cannot properly complete the thermal exchange process. Fortunately, you can simply hose off outdoor fins or carefully wipe down indoor fins -- just wear gloves because the fins can be sharp.
Bent fins is the second type of damage. Once again, exterior fins are more prone to bending simply because they are more exposed compared to the indoor evaporator fins. There is a tool called a fin comb that can be used to carefully straighten the fins. Don't try to straighten them by hand, though, as you will get cut. Only use the tool.
Don't wait until there is a problem before servicing your fins. They should be inspected annually, such as during your professional yearly tuneup, so that dirt is promptly removed and any damaged fins are straightened. You should also check the fins monthly during the cooling season to make sure they haven't become dirty.
If more intense damage has occurred, such as a broken fin or heavy rust, your AC tech may need to replace the coil panel completely. In some cases, though, they may be able to remove the rust and seal the metal to prevent further degradation.
Contact an AC system maintenance service for more assistance with your evaporator or compressor fins.