Hi everyone,

I have probably what will be a stupid question. I've previously worked on mostly HVAC but in my new job I look after a few freezer rooms and cool rooms.

I repaired a gas leak on a freezer room (R404A) and had a bit of trouble getting my head around charging it.

How do people what out what pressure the unit should be running at when compared to the temp inside the room?

Say, I want a -20 degree freezer room, how do I work out what SST/pressure I want?
During the charge when the freezer hits -10 degrees, how do I know what my SST should be?

I charged the freezer to a full sight glass and a 6K superheat but I was still confused as to how other technicians over the phone knew what temp my freezer was just from me telling them the SST/pressures.

Also, does the answer to the above question also apply for cool rooms, etc?

Once again, sorry for what seems a straight forward question - I'm trying to wrap my head around refrigeration and learn a bit before my next service call.

Thanks