One Ton of refrigeration is defined as amount of heat (288000 Btu's) required to cause a change in state of one ton of ice to one ton of water at 32 degs. F in 24 hours.
A/C units are rated by Btu/hour ratings. A one ton unit is rated as 12000 Btu's (288000/24) The average factory installed auto A/C unit is rated at 1-3/4 ton.
