Young puppies are notorious for chewing on almost anything they can reach. Depending on your puppy's personality, it may even claw or scratch at household objects. While cords and furniture legs are common victims, even your air conditioning unit is not safe. To protect your AC unit from your puppy, you will need to progress through a series of steps until you find a technique that works for you and your puppy.
Give your puppy a variety of dog toys designed for him to chew. This will help to distract him from chewing on random household objects, including your AC unit. Praise your puppy when it chews on these toys. To make them more enticing, buy the kind of toys that are hollow and fill them with peanut butter or your dog's favorite treats.
Move your air conditioning unit out of reach of your puppy if the unit is portable. This should protect it from all but the most stubborn puppies. In time, you can move it back into its original place once your puppy is a bit older.
Place a dressing screen or other decorative obstruction in front of your AC unit if you have room. For many puppies, out of sight really is out of mind, and your air conditioner may be safe if you hide it from view.
Booby-trap your AC unit if you can't move or hide it. Try placing a few coins in an empty soda can, then putting a piece of duct tape over the opening. Put this homemade rattle on top of the AC unit so that it is partly over the edge of the unit and any disturbance causes it to fall. The next time your puppy chews on the AC unit, or claws at it, the can will fall and make a loud noise, startling the puppy without hurting it. This method makes your puppy associate the bad noise with the air conditioning unit instead of you, which it would have done if you yelled or directly punished it for chewing on the unit.
Spray or coat your air conditioning unit with a foul-tasting substance. This is another alternative to try and keep your puppy away from the AC unit. Several products designed for this purpose exist, and any pet store carries them. Despite the bad taste, these products are non-toxic and not harmful to your dog.