Ok, have an 09 Sport with 95k miles, AC has worked ok. Lately, my gauge (AC Pro), reads right on the line between 'green/blue' (or add/full ) and the compressor is cycling about every 15/20 seconds. When the compressor is on, the needle jumps to half way 'full.' When the compressor shuts off, the needle drops to between 'add/full' Question is......should I add some AC Pro, and if so, do I pull the trigger and keep it pulled, or pump the trigger until the needle stays in the middle of 'full'. Thanks for info.

 

Suggest looking at this video before adding any refrigerant to your car. Make some temperature readings first before proceeding.
Really need to be using a proper gauge set that reads high and low side pressures to diagnosis your car. Most diy people don’t have proper training to do this. Just throwing refrigerant in your car is not a good idea.