generally the way it works is there is a pressure sensor thats connected to the pcm and the pcm controls fan operation depending on pressure and engine temp. so the only way to really see is with a bidirectional scanner.
as far as the leak, a leak is a leak. some say the compressors are designed to let some out but thats not true. i put some nitrogen in and listen, and squirt around suspect areas with dishsoap and water in a spray bottle. any bubbles and you have found your leak. you could use refrigerant but its not really that cheap and environmentaly correct. once you fix the leak it needs to be vacuumed down a couple times and charged
1998 Bonneville SSE
2007 Monte Carlo LT-KYB, Clarion, Polk audio, Kicker
1999 Yukon SLE-KYB, Air lift, Reese dual-cam, Tekonsha
1987 Firebird-355/th400-nothing stock