If you measure the CFM across the cooling coil and measure the dry and wet bulb on the coil and off the coil you can determine the total BTU EX: say you have a three ton unit
The rule of thumb is 400 CFM/ton so you have 1200 CFM
The dry bulb is 75*F and the wet bulb is 60*F on the coil and 55 DB and 54 wet bulb off the coil. Plotting on the psycrometric chart gives an enthalpy difference of 3.74 btu/lb of air and a sensible heat ratio of 0.81 and the specific volume of the air is 13.653 cu ft/lb so if you have 1200 CFM/13.653cuft = 5,777 lb hr or 95lb/min. The total load at those conditions is 33,890 btu and the sensible cooling at 81% = 27,500 btu and the latent is ~6,285 btu. As I said as conditions change so does the output on capacity and if you want to know what it's capable of doing you need the mfg specifacions which should be rated at ARI specs
