Um.... you need gauges to verify that you have refrigerant. Maybe the universe is trying to tell you something. The low pressure switch will be closed when the engine is off if you have any charge at all. These do not fail often, but they do fail, so if you test the switch for continuity and don't get it- AND you know you have static pressure at around 100 psi depending on the ambient temp. Then it's bad.
AFAIK, you just press the tabs, wiggle and pull. It's probably stuck from not being unplugged in 13 years. You are unplugging the one under the fender- right?
General AC Troubleshooting and Repair.