Keystone air conditioner displays CF after a certain number of operating hours.

Note: CF is typically a maintenance reminder, not a fault.

Steps:

• Remove and clean filter: Slide out the air filter, wash with mild soap and warm water, rinse thoroughly, and let it dry completely.
• Vacuum coil: Gently vacuum the front of the evaporator coil to remove surface dust.
• Reset indicator: Press and hold the FILTER RESET or corresponding button (refer to user manual) until CF clears.