Perhaps a make and model number will get you help to how to dismantle this unit.
Not only does the bottom have to be cleaned but the internal dusting also has to be cleaned out and the blower wheel.
You seem to be missing the metal duct that goes from the blower output to the back on the unit.
FYI: When you switched to 3 wire did you attach the ground strap from Neutral to the machine chassis.
If not you should have.