They are called 'fins' . If you can take the unit outside...then spray the inside fins and the outside fins with some degreaser preferably..or, some spray detergent. Allow it to soak in for 5 minutes...then, hose them down good but dont crush the fins with too much water pressure. Then, tilt the unit up so the water drains out for about 30 minutes. Then reinstall it in y our window.
If you have to clean the fins with the unit in the window..then, use some spray detergent with a wisk brush and get the dirt and junk off. Then, to rinse it, you can just spray some water out of a spray bottle on the fins -- the water will run toward the back of the unit and drain outside.
Make sure the electrical is disconnnected before you do any cleaning or rinsing.Always allow 30 minutes for the water to drain .
Dave
"Hey....have you hugged your Guage-Manifold today ?!"