I just get after them with a power washer. The one we have at work has heat but either way it will blow it right off there no problem. Maybe soak it with something first like 409 or fantastik...just don't open the air filter cover and spray it right in there or anything...and definitely wash out and re-oil the filter element when you're done. Also run it after you spray it, get it hot, let it run for a few minutes so the coil and the rest of it has a chance to dry out. That's just what I do.