The a/c was working great till we came back from a short vacation. We tried putting freon in it, but the guage immediately went to the red zone. The compressor looks like it's running. It's 91 degrees out and everything else seems to be working.

 

You, shouldn't have added refrigerant. You should always properly diagnose the problem first. Something else may have caused your A/C to quit.

Do the radiator fans turn on when the A/C is turned on? If not, unplug the harness going to each fan and plug them back in.
What does the temp gauge indicate when the engine is warm?
Do you have a Check Engine or Service Vehicle Soon message/light on?