The pressure switch is not a valve, just a port for the switch similar to a gauge. You had said you were getting 12 volt to the clutch which ruled out a bad switch. The shraider valve for the gauges is just a port valve and does not effect the systems operation. The pissssst is just the coolant escaping while removing the gauge hose. Always a good idea to push the hose towards the port while unscrewing the hose to minimize coolant escape, and be careful as the liguid coolant can freeze skin and seriously damage eyes.
The compressor has valves in it that if in the right position could prevent coolant gas from passing, and the evaporator will have some sort of restrictor / valve to lower the liquid lines pressure which could under certain circumstances prevent gas from passing (though there is usually a bypass here to equalize pressures when the system turns off).
It is possible that the coolant liquid locked the compressor momentarily (compressor is designed to pump gas not liquid), causing the delayed start (though this would cause the belt to slip and squeal), or the liquid had not converted to gas yet as static (not pumped up into pressure) liquid coolant can have less pressure than gas and not activating the switch at first. And, it is possible that removing the high pressure hose jarred a bad connection at the clutch wire.
I would check the clutch wire, if ok, let it go as maybe one of the other causes which fixed themselves.
Sorry for taking the long road.