Why are the units measured in tons? Is it heavy?

“Ton” is not the weight of the unit. Example: A 3 1/2 ton unit means there is 3 1/2 tons of cooling capacity. It is a unit of measurement used for determining the cooling capacity. 1 ton is equal to 12,000 BTU’s per hour. It will not fall through your roof. The actual weight of the unit is considerably light. Air conditioner capacity is rated at 95°F outside with an inside temperature of 80°F and 50% relative humidity. Each ton of air conditioning is nominally 12,000 Btu/h (this comes from the fact that it takes 12,000 Btu to melt a ton of ice). While an air conditioner may be called a three ton unit, it may not produce 36,000 Btu/h in cooling. There is a wide variety of actual capacities that are called “three tons.”