The outdoor unit houses the compressor and condenser coil, and its exposure to weather makes it prone to a different set of issues than the indoor unit. Dust, leaves, and airborne debris settle on the condenser fins over time, restricting the airflow needed to reject heat from the refrigerant. Bent fins, often caused by pressure washing or accidental impact, further reduce surface area available for heat exchange and should be straightened with a fin comb rather than left compressed.
The fan motor on the outdoor unit pulls air across the condenser coil, and a failing motor or worn bearing reduces this airflow, causing the system to run at higher pressures and temperatures than intended. Placement matters as well; an outdoor unit installed in a location with poor ventilation, such as a narrow shaft between buildings, recirculates its own hot exhaust air, which lowers overall cooling efficiency regardless of how well-maintained the unit is. Rust and corrosion on the coil and chassis develop faster in humid or coastal environments, so units in such conditions benefit from more frequent visual inspection.
Keeping at least the manufacturer-recommended clearance around the unit supports both heat rejection and easier access for future servicing.