M/H Winter vent cover

The only time that I have found a fridge not to cool properly has been when it was well below freezing and the caravan was sat on the drive. As soon as I had put the 'van heating on and raised the internal temperature the fridge worked fine despite the outside temperature.

My fridge manual tells me when I should fit the covers. One reason is the external temperature as mickysf says and the other is when washing the vehicle to stop water getting in through the vents. Other makes/models may have different reasons.