I went to Lowes and got a can of coil cleaner. I sprayed it heavily, let sit for 20 minutes, sprayed with jet stream nozzle. Got it looking pretty good. So I sprayed the cleaner again and put back together. Where I was getting only about. 220 ft/min flow on hi I am getting around 610 on hi at all 4 vents.If you pulled the dash - out a new one in, OEM please because they last.
I cleaned mine within the dash through the fan opening with simple green, water spray and a small vacuum cleaner attachment. Worked out good.