This is an extreme case, but all evaporators collect trash & dirt. With the evaporator out of its housing like this, it's easy to vacuum it off and then hose it out. Be careful not to fold the fins over.
Note that this system is still fully assembled & charged with refrigerant. There is no need to vent refrigerant for this or many other operations. The complete refrigerant system can be removed/installed while fully assembled & charged.
To prevent reoccurrence, add screens to the fresh air intake under the wiper valance. To keep leaves out of the passenger side (where the HVAC intake is) and force them to the unused driver's-side drain, add screen at the top, just below the wiper valance:
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To keep leaves out of the ventilation system, add screen inside the cowl by removing the wiper valance & working through the rubber plug under the antenna:
See also:
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