2oldman, with the numbers you are giving you are recirculating cold air. In otherwords, a lot of your cold air is getting sucked back into the intake. That is the only way your indicated delta T you are stating is possible. Or your measuring device is incorrect.
The difference between a 13.5K and a 15K is 1.5K. An air conditioner really is a heat remover. So the 15K will remove more heat. (BTU is a measure of heat) It does this by moving more air across the condenser and the evaporator, having bigger tubes and a larger compressor and probably a different orifice or expansion valve. I am certain many things are different between the two units. The temperature difference (delta T) between the intake and the outlet will always be 18-22 degF on a properly functioning unit with the technology we use today. The air mover in the larger unit will probably move more air.
