In 2oldman's case the split temperature reflects a leak between the intake of the evaporative coil and the standard from-room intake area. I'm guessing there is a flap loose in that area that allows the cold air flow to cycle back through. It is well established what an air conditioner's Delta T can be and the information posted about latent heat and wet bulb is also accurate.
To ask an A/C technician if he has used a temperature measurement device is kind of insulting to the Tech. It is one tool that is commonly used. The actuality is that Delta T will always fall close to 20f.
