AC low pressure code

Hi

95 Concours, I have been getting an intermittent A047 low freon code.
I reset it and everything is fine for a long while.

System blows cold and works well.

The code comes often now.

Funny thing is if I just let the car idle with AC on it does not code?

How can I prove or disprove the sensor and or wires to it?

Does the system need to be evacuated and recharged to change the sensor?

Thanks