Tips on charging refrigerators with 134a?

I have a friend who runs a small appliance repair business. He wants me to charge refrigerators that he’s repairing with R134-a. I’m Universally licensed to handle all types of refrigerant, and am familiar with charging practices, I know I’ll have to use a piercing valve and I have my own set of refrigeration gauges. What I’m wondering is, are there any general tips or rules about how much to charge to for a refrigerator? I’ve charged A/C units before but never done a refrigerator, and it seems you only have to hook up to the low side but I have no idea what i’m doing past that, such as how much to add or what pressure/temperature should be attained, or if there are any visible signs to watch for like frost on the lines. Any tips would be greatly appreciated. :)

The plate on the compressor will tell you the weight of the factory charge. Reclaim all of the original charge, pull a vacuumm and weigh it in.

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