What is the best type of fire extinguisher to use on a fire caused by a shorted air-conditioning unit?

Using a carbon dioxide fire extinguisher on a fire caused by a shorted air-conditioning unit is the best choice because carbon dioxide is a clean agent that suffocates the fire by displacing oxygen. Short circuits can lead to electrical fires, and since CO2 does not conduct electricity, it is safe to use on electrical fires without the risk of electrocution.

Additionally, carbon dioxide extinguishers leave no residue, which is advantageous in an electrical equipment environment like that of an air-conditioning unit. This minimizes the potential for damage or further complications. In contrast, water could be dangerous as it conducts electricity, and using foam or soda acid extinguishers isn't appropriate since they are primarily designed for flammable liquid fires or specific types of fires, such as those involving combustible materials or certain chemicals. Thus, the use of a carbon dioxide extinguisher effectively addresses the risks associated with fires stemming from electrical equipment.