It's normal for pressures to jump around. Two things which affect high side pressure are compressor output and airflow across the condenser. Both of these vary independently. Compressor output varies with engine RPM, airflow across the condenser varies (mostly) with the speed of the car. So it's normal for pressures to spike pulling away from rest - compressor output is high, airflow is low. In contrast, pressures should stabilize at a 40MPH cruise - compressor output is moderate and steady, airflow is good. What is your high side pressure under these conditions?

When you see 47 degree air temps, what is the fan speed. On high fan that is quite good for an old R4 car. If medium or low speed, not so much.

Have you looked into the fresh/recirculated air flaps? I'm not as familiar with the 126 setup, but if you are trying to cool fresh air rather than reciculating at least the majority, you won't get very good cooling or dehumidification.

- JimY