Hi I am new to this field.
I am familiar with charging a system using superheat and subcool levels based on manufacturer's performance chart.

What do you guys do when the chart is missing or ruined by age/water/bugs.
I am talking about residential units less than 5T.

Is there safe, general rules to use for SH and SC?

How about TXV vs. cap tube systems?

Would the levels be different for R-22 vs. R-410A?

I know it is not the best way to ball-park it, but if in a jam it'd be good to know a safe level to start.

Thanks for your help.