Make sure the can is inverted, so that the the liquid is forced into the system. If you pressurize it with gas, you'll have a heck of a time trying to get liquid in there without purging or jumping the compressor.
Originally Posted By: dishdude
Put the can of refrigerant in a small bucket of warm water to keep it from freezing up.
Yes, warming the can will help to motivate the liquid refrigerant out of the can if it stalls (compressor off method). Again, always charge with the can's bottom-end up.
Also, double check your static pressure (against an R134 static pressure/temp chart), to see if you have any liquid in the system right now. If your STATIC pressures are inadequate, it will indicate that there is no liquid present in the system and you will without a doubt need nearly a full recharge. If there is liquid refrigerant present, you'll need a top off only.
If you do it yourself, just be careful. No one will die, no one will be injured (IMO one would really have to try to be injured) you just need to read up a bit, understand what you read and take care in doing it.
best of luck