1985 W126 AC Problems

[BioDieseLandon]

So here is the deal. I just charged my system with R12 because its getting pretty hot out and my AC has never been fully functional. The system works but the problem is when I am driving down the road on the highway my compressor consitently cycles on and off about every 10 seconds. I put a jumper on the low pressure switch and tried to charge it but it still cycles on and off. Could it be an issue with the climate control unit? Also when the compressor is running the high side exceeds 400 PSI...what is the proper operating pressure for R12 on these cars? Also note that my 12 volt condenser fan never comes on...