Here's the scenario: On a True GDM-12 with 9 oz charge of 134a for example, I will weigh in the proper charge on the nameplate but often find it necessary to bump in a little more(1-2 oz) or so due to different drier, comp, hose length,etc. to end up around 15*f vsat at around 34*f box temp give or take. Now that I have switched to digital with the SMAN3 I decided to call True and ask for recommended superheat numbers. This is where it gets interesting.
The first tech I spoke with immediately said 45-55* superheat at operating temp measured at compressor. So I began charging a few units that way but they seemed a bit overcharged to me so I called back and got a different tech. He said " a capillary system can't be charged by superheat or subcooling only by weight or pressure." He suggested 14-17psig suction and 135-150 head, but couldn't commit to a target box temp for those numbers. As luck would have it, I had one brand new GDM-12 still crated so I committed the cardinal sin and opened the system. I used stubby analog gauges and the pipe clamps on my sman3 to get my numbers. I checked it in an 86* warehouse and in the 75* office and found at 33* box temp low side 19/17 and high side 160/140 Superheat 65/61 measured at compressor.
So it seems both techs were wrong and my old way was in line with factory specs. Just want to know anyone else's experience with these type units and what is the proper way to charge them?