In an air conditioner, 'ton' refers not to the weight of the AC unit, but rather its cooling capacity. It is a measurement of ...

In the context of air conditioners ... A 1-ton AC can cool 12,000 BTU/hour (British Thermal Units). A 1.5-ton AC provides 18,000 BTU/hour. A 2-ton AC delivers 24,000 BTU/hour.