Yes, this is another thread asking about superheat! However I assure you I have worn away that search button to try and get answers & I'm almost there!

My main source of business is in commercial refrigeration, such as kitchen refrigerators, bottle coolers, cold rooms, beer cellars and the occasional A/C systems. Over the years I try my very best to use available weights to weigh in the refrigeration, but with beer cellar systems, cold rooms & A/C system installs I need a reliable way to charge the systems. Up-to now I've been doing it by sight glass & touch, but I understand that's not the best way of doing it, so I've been looking into superheat & sub-cooling. Besides I understand It's a useful indicator when diagnosing faults in the refrigeration process.

Using most of what I found on here I'm now at a point where I'm confident how to measure actual superheat on a system. However I'm now struggling to understand how to calculate target superheat.

I was taught that superheat is the where the refrigerant has completely boiled off, occurring at the end of the evaporator, and is required so that no liquid is entering the compressor. So in my mind if you can achieve a couple of degrees above the boiling point of the refrigerant then you have adequate superheat. For example if I have an r134 system, and messure the super heat (temp measured on suction - saturation temp from the gauges) anything above -26c (Boiling Point of r134a) would be adequate.

So isn't any temperature above the boiling point of the refrigerant adequate super heating, and thus the target superheat?

I'm guessing I'm totally wrong in regards to target super heat, because on the few guides I have found wants superheat to be between 5C - 10C, which is far above the boiling point of any refrigerants, and these guides don't mention any variance in refrigerant types, so I guess I'm missing something! However I'm here to learn and I hope you guys can point me in the right direction!

Thank you kindly

Jim