Residential Refrigerator – What to do with the side Vent?

On some fridges you might wish to leave the vents open to encourage better cooling, Others, that won't work

I wold visit the hardware store, get a sheet of thin aluminum and cut it to match the opening,, Cut out for the latches an install it (perhaps with weatherstripping or caulk) behind the existing louvered cover.. The result will look exactly like it does now.. but will not pass air.