AC R134 Conversion: Single Pressure Switch - Use an O ring? Tape?

[Mahalaleel]

I must have lost it. I ended up putting a spare o-ring in there to test with vacuum and pressure, and now it's good to go.

In the end I replaced:
Condenser
Receiver/drier...

[Mahalaleel]

I'm going through my entire AC system to get it back to 100%

I have replaced/rebuilt almost everything. I am converting from dual pressure switches to a single pressure switch...