The EPR is a evaporator pressure regulator. If you have them on the suction lines there will be a dust cap you remove to access a allen screw. Adjusting will regulate the evaporator outlet pressure.
I dumped the 404 that was in it and pulled a good vacume and cleared the sight glass with new refrigerant. Im still getting an iced up line including the compressor but at least ive eliminated moisture being a problem. Im running 25 on the low side and 250 on the high side. Ive got a 10 degree line at the evaporator outlet and its frosted over the whole line. Still I cannot get the box temp below 30 in any of the 3 evaps. Im down to either having to adjust these expansion valves or finding this EPR valve you are speaking of. Do these types of valves go out of adjustments often??? Do you know if all systems of this type has this valve installed on them? I could not go further with this today because I had to go to a different restaurant and replace a condensing unit on another drawer system...lucky me.
Is your discharge line Hot? If not climb in the cases and try to figure out which valve is overfeeding. Also check out the evap fan blades. Alot of guys end up throwing a little 3incher on when it needs a 5.5".
The ones I installed for them did not have EPR valves. They also used transflow blowers not standard fans. Agree that w/ epr they would have worked much better but I was not the engineer and they wanted to keep cost low, didn't seem to consider future service cost.
I've been working on denny's freezer/fridge drawers for a couple years now. always a pain in the arse. The one im working on currantly has 3 compressors on the roof. 2 of the compressors are running multiple fridge drawers. About 4 a peice. The other compressoor is running just one freezer drawer. All 3 compressors have liquid acumilators. the freezer drawer system has a suction line acumilator also. They all have pressure controls to cut out on pressure drop. All the fan coil's have silinoids. the fridge drawers have t-stats inside the drawer units. the freezer draw has no t-stat and is controlled by the pressure control that shuts the copressor off when the unit dropes to a pressure on the low side that correlates to the temp inside the freezer. They all have defrost controls.
I had the freezer drawer down to 5* f threw last fall and winter. now that it is warming up outside it is having problems again. started by cleaning the coils outside that were filthy. temp still not low enough. now im back to counting turns on the expantion valve and playin with the charge. I hate these units.