It could be low on refrigerant, or it could be a bad sensor.  Back-probe the
pressure sensor connector (on the discharge line, near the compressor - it's
a 4-way connector) on the dark blue wire with the engine running and the A/C
turned to max.  If you get no volts, or 5 volts, the sensor is bad.  4.5
volts indicates a properly-operating system, while less than 4.5 indicates
low pressure, and anything above indicates high pressure.  If low or high
pressure is suspected, verify with a set of refrigerant gauges.

If warranted, the sensor can just unscrew.  You won't lose refrigerant -
there's a valve built in to the line to prevent that.  Make sure to use a
new O-ring and lube it with the proper oil if you do change the sensor.