A/C air is not cold

I noticed that air was not cold enough a few weeks ago. One day it was blowing hot air on A/C, now it is just ambient temperature out of all vents. Compressor clutch is engaging on A/C, radiator fan is spinning, radiator is clean, belt is okay. Checked Freon pressures at about 77 degrees:
-Static with engine OFF: low and high around 80.
-Engine ON, A/C on MAX: low 5, high 100. Revved engine up to 2000 RPM no changes.
-Just for fun, set A/C to 70 degree on both driver and passenger sides and blower speed to medium (3 bars) no changes.
-Engine still running, A/C to off clutch disengaged, low 80, high 90.
-Turned engine off same as above.
Seems like if both sides static pressure is about normal, there is enough Freon? On A/C, both sides are lower than normal, but clutch and radiator fan are okay. What's the most likely problem and what other tests I can do before taking it to a mechanic or trying to fix myself? Is it worth trying to add Freon? Thank you.