I was getting a clicking noise from under the dash which indicates a bad HVAC Actuator. The teeth on the gears eventually break off or strip and it wont work right anymore. Well after removing it and splitting it apart I noticed a tooth on the drive gear was broke. I also noticed that more than half the drive gear doesn't even come in contact with the blue gear. So I ended up sliding the gear off the silver metal part with the hole in it and rotating the gear 180 degrees.....pressed it back on...put it all back together and no more clicking. Cost= a couple hours.