The system is a cold roombox that holds 39*F. It has 404-A refrigerant. The condensing unit sits about 22'-28' above the evaporator. There is a reciever, accumulator and I think there was a EPR valve at the compressor. Can't remember. The condensing unit sits in a rack with two identical units below it. They are water cooled with head pressure regulating valves. There is a hot gas line that runs down to the box. I could not locate the solenoid valves, I think they got sheet rocked in above the box. So I don't know how they got piped.

The sight glass was flashing. My first question is how do you charge a system like this? I have read that you cannot charge a system with a reciever by sub-cooling. Is that correct? I was told that the vertical drop of the liqiud line will cause the sight glass to flash. Is this correct? Also being a blend the sight glass may flash a little to begin with.

One thing I did notice between this unit and the other two was that the sight glass was not flashing on the other two. I expect it was because of the way the liquid line was piped. On the unit with the flashing SG the LL comes out of the reviever and travels horizontal until it makes a drop. The SG is piped in the horizontal line. On the other two that do not flash the LL comes out of the reciever and is pipied up about 1' to 1.5' before it runs horizontal and then goes down. The SG is located in the vertical prtion of the LL. My second question is can piping the SG this way in a system like this were the condensing unit is above the evap have the advantage of indicating when the system has a correct charge?

What do you guys think? Thanks for the help.