from the side of the can... troubleshooting: if compressor does not engage, add half of can to low side and wait 3 minutes and check again... if compressor still does not engage, repairs may be necessary.
you're feeding the can into the low side line of the system. the clutch doesn't engage, because there isn't enough pressure to kick the clutch in. once you force the pressure into the low side of the system, it's supposed to be enough pressure to engage the clutch. That said, if it doesn't work, then you have a leak, or something physically wrong with the compressor clutch. the clutch shuts off the line in a refridgerant leak to protect the compressor. I'm sure you know most, if not all of it, but if that part doesn't work, then you're in for something more than a quick fix.
