300 SDL/ R12/ AC with 60F at vent

[werminghausen]

I have redone the entire AC of the SDL 3 years back (including evaporator!), all parts new basically.
I experienced high vent temperatures lately and thought it must be low charge, bought some R12 and tested, but couldn't find a low charge. So I have no idea what might be wrong. Maybe someone can help:
testing:
aux fan on high, fan inside on high, temp dial on low, recirculation on, at 90-95F ambient i can read low/ high at following rpms
idle: 40/180 or 38/ 180
at 1500rpm: 30/200 or 28/205
vent temperatures: devastating 60 F
I have no clue why there are not 45F at the vent. charge might be slightly low but.....I don't think it makes such a difference.