"Please remember 50% of the fun on these cars is solving the technical riddles.The other half is pulling up to the dealer to buy parts and watching people pick up thier cars at service."
You can imagine my fun then... watching DIYers play with these simple systems (vbg LOL).
The pressure switch is on the drier and should have connected the circuit with a very small ammount of pressure. The original switch was probably just a low pressure switch (for preventing the compressor from burn-out pumping a dry system). The new switch will be a low/high pressure switch which will prevent damage from over-pressure; very necessary with R134a systems.
The system will have to be discharged to remove the switch. Check the circuit at the switch to be sure its the problem. If its the problem one side will be hot (battery voltage approx) and the other side not.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician