Hello and thank you for your time. I am a 2nd year apprentice from Aus and wanted to ask something thats been bothering me and none of the tradies at work have provided a good answer. How do I know how much gas I should be charging into a system? The tradies just say to keep slugging liquid until the sightglass seems full but i want to understand what im actually doing with the system. What should my gauges read and how do i know that my gauge readings are "correct" if i can see a full sightglass? What is a "correct" gauge reading for an underbench, a coolroom, a freezerroom etc and how can i learn to apprehend the differences quickly and independently using my brain and not a cheat sheet?

Also, what exactly is Temperature Difference, it's importance and how is it established? Is it a feature of design? If so, how can I apprehend that using information from the system I'm looking at?

Thank you. I really dont want to be stuck scratching my head when the boss eventually puts me out on the road so as much good, clear info you can give me the better. TAFE isnt much help either :S