Voltage at A/C low pressure switch?

Hello, it depends on what Switch/Sensor you are actually checking, the A/C Low pressure Switch operates at 12v, it will be a 2 wire switch, whereas the A/C Refrigerant Pressure Sensor is a pressure transducer and operates on a 5volt Reference and will be a 3 wire sensor, The Low Pressure Switch is either open or closed, the pressure sensor will read various pressures depending the 0-5 volt signal, but 11 volts sounds low, I assume you are checking this with it unplugged and the Key on, Engine off?
I'll post some service info for you and some wiring diagrams so you can check to see where there might be a corroded connector going to the pressure switch, and that's why you're reading 11volts.

Do you have an Auto or Manual A/C HVAC system? Auto you can set a temperature and the HVAC module will keep the interior at the temperature automatically.

Okay, looking at the 2000 model, it does not have any pressure sensors, it has 3 pressure switches that all work on 12v, on/off type, so that's the reason for seeing a sensor with 5volts on the 2003, but the 2000 looks like it should still get 12 volts on the pressure switches.

This is the 2000 model with 3 different pressure switches. So depending on the wire colors for the switch you are getting only 11 volts at, they all get their 12volt references from the PCM, so it could be corrosion in the PCM connector, or in the wire coming from the PCM, I'll find a pinout diagram for the 2000 PCM if you want to check it.
Here is the 2000 PCM connector C2 pinout and locations of wires for the different pressure switches.