Nov 04, 2021 · Many reverse cycle units are also available that uses a compressor for heating and cooling. This method is more efficient and is most popular when it comes to caravan air conditioners. Size. Typically, there are 2 types of air conditioner sizes, i.e. 2-2.5kW (suitable for vehicles with 5meters length) and 3kW+ (for vehicles up to 7 meters long).