How to access evaporator to chage orifice tube - eldo 97

For my eldo 97, the clutch turns on but low side pressure remains about 100psi. I guess it is freon blockage at orifice tube. I think it is in the evaporator. Any idea how to access the evaporator and how to change the orifice tube. Is the orifice tube welded there or just screwed in. How easy it to access the orifice tube?

Thanks
John