Dixie narco pepsi machine

I have a 1999 dixie narco pepsi machine that the evaporator keeps freezing up on.  It is freezing (frost on outside of tubing) at the point where the liquid line just enters the evap coil. The complete evap coil does not freeze thoughtThis was freezing was happening before I broke into the system. System looks in virgin state.  I soldered a service valve to the low side of the compressor so I could pull a vaccum on the system and add freon.  Pulled vaccum for @1 hour, let it set overnite and held.  Put 7.5 oz of R134 in system based on service tag on unit.  Both the evap/condenser fans are working properly, evap is clean, thermostat is new.  Low side vac was @ 17 psi.  Compressor seem to be excessively hot to touch.  The high pressure line exiting the compressor reads @188 with IR temp sensor.  Compressor has never kicked off due to overload switch.  Any ideas what might be causing my problem.  Thanks