Fall brings a specific seasonal challenge for outdoor AC units that summer doesn't: falling leaves and seasonal debris accumulating around and inside the unit, right as cooling demand starts to taper off but before the system is done working for the year.
Why leaf buildup is a real problem, not just a mess
Leaves and debris that accumulate against the outdoor unit's fins restrict airflow across the coil, the same underlying issue that causes many of the airflow problems covered elsewhere on our blog. Wet, decomposing leaf matter against the coil over an extended period can also contribute to corrosion, similar to the pet-urine corrosion issue covered in a separate guide.
What to actually do
Clear leaves and debris away from the unit regularly through the fall season, rather than letting them accumulate until spring. Gently rinsing accumulated debris off the coil fins with a garden hose (power off, low pressure) periodically helps as well. If leaves are landing directly on top of the unit from an overhanging tree, trimming back branches to reduce that buildup is worth considering.
What not to do
Avoid fully covering the unit to keep leaves out, covered below in more detail, since it traps moisture and can create the exact corrosion and pest conditions you're trying to avoid. A properly positioned clear area around the unit, checked periodically through the season, is more effective than trying to seal it off entirely.
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