Is A/C working normally?

Geezus Kareiaust. You don't figure delta T based on INDOOR discharge temp and OUTDOOR ambient. You figure it based on the DIFFERENCE between what is ENTERING the evap and what is LEAVING the evap.

But this sounds like a conversion from R12- to ?? is that right? Some of these conversions reduce efficiency, because the components are not optimized for the new refrigerants. R-12, unfortunately, was a VERY efficient refrigerant for certain things.