Unless it's new or recently cleaned... Go topside and clean it. Breaker off then pull shroud followed by evaporator coil inner shroud at front. Catalog the screws to put the right ones back.
Brush debris then spray both coil with 409 or similar.
Rinse clean with hose and fine spray nozzle. Use towels to keep rinse water out of coach. I use a license plate as deflector.
Find drain holes and make sure they are clean. Water you spray should drain fast.
Ducted? Make sure Defrost Sensor is in place. Run Fan On, and High
Non Ducted? You're a Beach Guy. No Freeze Sensor. Puts You in charge, set to High Fan only.
Clean Filters of course.
