This looks like user error. I recreated the room as described and was able to cool it down to -10 C with an outside temperature of 50 C.
Make sure the coolers face the right way (red outside, blue inside) and are powered, check if the building is properly roofed and dont leave the door open all the time.
Make sure the coolers face the right way (red outside, blue inside) and are powered, check if the building is properly roofed and dont leave the door open all the time.