Frigoboat Keelcooler Troubleshooting

[Katka]

Hi,
We have been working on our refrigeration system for almost one year now. We have had working Air Cooled Frigoboat system before. We expanded our capacity and added keelcoolers. We have now two systems - one for our freezer and one for our fridge. Both system have same size of evaporator plates and same keelcooler. The freezer has new compressor BD50. We reused our old compressor for our fridge. The compressor was working for 11 year. We disconnected the compressor and it sat for about one year. We connected both system and the freezer works perfectly. The fridge does not. The compressor seems to be running, we feel the vibration but there is not cooling on the evaporator plate. There is no frost or sweating. We don’t hear any noises of any movement in the plates. The connection are dry with no sign of leaking refrigerant.
My idea is to use the A/C gauge to measure if there is refrigerant in our system. Unfortunately we can’t find any information about the pressure value on high and low port. The Frigoboat boat people told us it is not information for regular person, only for license technicians. Also we were told that the R134a sold in for example Harbor Freight is for car AC only and can not be used in keel cooled system. We are now debating how to proceed forward.

If anyone has any information how to measure and examine the pressure in working vs non working system, please can you share it with us?

Can someone verify that the R134a sold in auto parts store is the same as the one used by refrigeration technician?

Thank you so much for all your help.