Foam paintbrushes are perfect for getting deep into the spaces between your air conditioner vents’ slats. They’re inexpensive and available at your nearest home improvement, craft, or dollar store. You could also purchase a set online. Combine equal parts of warm water and white vinegar. Try using lemon-scented cleaning vinegar if the smell bothers you. If you can’t find lemon-scented vinegar, add a teaspoon of lemon juice to your cleaning solution. Dab a foam brush in your cleaning solution and press it between your vent slats to remove dust and grime. Rinse your brush as needed to remove the debris it accumulates, or simply use another brush. Finish by wiping the vents down with a dry brush if you’ve left any excess cleaning solution. Wash your used brushes with warm water and a dab of dish detergent. Squeeze them out and rinse well to remove excess soap. Let them dry, place them in a plastic baggie, and store them in your glove compartment for quick use.

Summary:
Purchase a set of foam paintbrushes. Create a homemade cleaning solution. Insert the foam brush between each vent slat. Rinse and dry used brushes.