1988 Camaro A/C Question

[aldaran]

I finally decided to convert my old R-12 system to R134 and ran into a problem. The first thing I noticed is a noise coming from the evaporator core. It sounds like a loud humming and the car stops cooling. This happens when the vehicle's accelerator is pressed lightly. I replaced the compressor, accumulator, and orifice tube. I also flushed out the lines. Has anyone had problems converting to R134? Should I replace the core as well? I appreciate your replies in advance.