My temperature difference between my supplies and returns is only around 5 degrees F. I opened up my air handler to see if the evaporator coil was dirty, and it was clean -- but running the outside unit (condensor) without running the air handler, I expected the evaporator coils to get very cold - to ice up, right? Well they got cold, but nowhere close to icing, and I suspect that's the reason my delta-T is only around 5F.

So this is after I just had the refrigerant completely recharged -- what could be any other issues as to why the coil isn't ice cold?

Edit: I've cleaned the condensor fins already. The whole system is around 20 years old (I know, it's ancient)