Cleaning a Rooftop Unit Coil

Turn off the thermostat controlling the rooftop unit. Turning off the thermostat disconnects the rooftop unit's low-voltage control circuit.

Turn off the rooftop unit's electric disconnect switch, located on the roof near the rooftop unit. A disconnect switch sits in a weatherproof box that either mounts to the side of the rooftop unit or on a secure structure near the unit. Turning off the disconnect switch turns off the rooftop unit's high-voltage power source.

Clean the loose debris from the exterior side of the rooftop unit's coil with a soft-bristle hand broom, working the broom along the fin's grain.

Combine liquid coil cleaner and water in a pressurized sprayer's holding tank, using the coil cleaner manufacturer's recommended ratio. Many technicians use backpack-style pressurized sprayers when working on a rooftop unit; however, a handheld pressurized sprayer will work.

Pressurize the sprayer's holding tank, using the sprayer manufacturer's instructions. Usually pumping a pressurized sprayer's handle forces air into the holding tank, which pressurizes the holding tank.

Mist the exterior side of the rooftop unit's coil with the coil cleaner. The mist loosens the debris stuck to the coil's exterior.

Insert the pressurized sprayer's nozzle into the louver covering the coil's interior side. The louver usually attaches to the top of the rooftop unit and the fan motor mounts to a bracket below the louver. The sprayer's nozzle will fit between the louver's blades, eliminating the need to remove the louver for coil access.

Apply a liberal amount of coil cleaner to the interior side of the rooftop unit's coil. The sprayer will force the coil cleaner between the coil's fins and wash the debris toward the exterior side of the coil.

Rinse the coil cleaner from the rooftop unit's coil with water. Either fill the pressurized sprayer with clean water or stretch a water hose onto the roof. If using the pressurized sprayer, insert the sprayer's nozzle through the louver blades and rinse the coil from the interior side. If using a water hose, hold the hose's nozzle against the louver blades and direct the water spray toward the coil's interior side.