looks Full on Low Charge
If the person working on the a/c doesn't have gauges hooked up to the system, during initial start up and running of the a/c system the glass will appear full of bubbles and then go to a full coat of freon on the sight glass, not empty looking. This is where the gauges must come into play as they will give you a better estimate of just how much freon is in your system. Yes, you can look at your sight glass with the system off verses on and running and it will apppear full, but the pressure in the system tells you different. I was just determined to either blow the sob up or charge the system to operating levels. A full sysytem will not draw freon into it like a kid sucking on a malt, and that's how my system reacted once I induced freon to it. So yeah, don't trust your sight glass as it will not give you a good representation of how full your system is. Lesson learned, hook up the gauges and don't trust your vision.
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan