A 4 ton rooftop HVAC unit is a type of air conditioning system that is designed to be installed on the roof of a building. This type of system is typically used in commercial and industrial applications, as it is designed to provide a large amount of cooling capacity in a relatively small space. The system consists of a condenser, an evaporator, and a fan. The condenser is responsible for taking in the hot air from the outside and cooling it down. The evaporator is responsible for taking the cooled air and circulating it throughout the building. The fan is responsible for pushing the cooled air out of the building. The 4 ton rating of the unit refers to the amount of cooling capacity it can provide. This is typically measured in British Thermal Units (BTUs) per hour. A 4 ton unit is capable of providing up to 48,000 BTUs of cooling capacity per hour, which is enough to cool a large area.