A heat exchanger is apart of any thermal transfer device and generally works by increasing the surface area so that a metal or liquid heat sink can cool down faster. Frequently, a liquid heat sink such as a polymer refrigerant will transfer heat to a metal heat sink which must then cool down with fins and a fan that blows regular air over the condenser heat exchanger.
The entire refrigeration system might range in efficiency, especially in the summer when it is more difficult to dump heat into an environment that is already fairly hot. The best way to maximize efficiency is to make sure the fins of the heat exchanger are properly aligned and free from obstruction. A secondary issue is to routinely check the refrigerant, although it is rare for refrigerant to leak in a regularly inspected system.