How do I know my Gram fridge is working properly?

We have just perchased a second hand commercial unright Gram fridge but when we got it back it didnt work. We have had it repaired, new comdenssor/compressor unit and a new thermostat.
My question is this the fan/motor sounds like it's running all the time and sounds too loud to me. It does stop when you open the door. Is this normal for this motor sound to be there??