The low pressure switch in an A/C system cannot be manually "switched" on or off.
most A/C systems have 2 switches. Both of these switches are "switched" by the pressure of the freon in the system.
One is located on the high side of the system, and the other is on the low side of the system. The one located on the high side is a normally closed switch that opens the A/C clutch circuit and shuts the compressor off when the high side pressure gets dangerously high - usually around 350 - 400 PSI. This keeps you from having an explosion in the event that the hoses become restricted for any number of possible reasons.
The low pressure switch opens the A/C clutch circuit and shuts the compressor off when there is not enough pressure on the low side of the system to safely operate the system. usually somewhere around 20 PSI. The compressor is oiled by oil circulating along with the freon in the system. If the freon leaks out, the pressure drops and the oil cannot circulate because there is not enough freon to push it through the system. So the low pressure switch shuts the compressor off to keep the compressor from blowing up due to oil starvation.
Failure of these switches is very rare. Almost every one that I have replaced was not because the switch didn't switch, but because it was leaking freon.
If your low pressure switch is keeping your A/C compressor from running, it is most likely that the system is either out of freon (due to a leak somewhere in the system) or because it is unplugged.
Your Nissan is equipped with a "Dual Pressure" switch. it does the job of both switches by opening under extremely high pressure as well as extremely low pressure conditions. it is located beween the front grill and the A/C condensor near the Accumulator just to the right (as you are facing the front of the car) of the right headlamp area. See picture.
To determine if this switch is functioning properly, you must hook-up an A/C pressure manifold gauge (to find out what the actual system pressure is) and use a volt/ohm meter to determine if the switch is opening and closing under the correct pressures.