With the approaching winter, homeowners are preparing their Furnaces and Fireplaces and at the same time putting their AC condensers on snooze for a long winter break. For winters, you must have heard of the importance of covering the condenser unit since not covering it damages the unit, particularly as the environmental factors make their influence. But we can say it for sure that you must have heard half of the tip. While covering is fine, fully fledged covering is not a good idea and there as convincing reasons why;

- Moisture in a fully covered unit 

The compressor unit develops moisture because of high humidity, rain, snow or other climatic conditions. This moisture easily gets dispersed when the unit is not completely covered and get sufficient sunlight. In the case of the fully covered unit, moisture will still find a way in but will not get away easily once it reaches in the inside of the unit. Long presence of moisture, as you can guess, will contribute to producing rust and mold on the unit and corrode the compressor parts. 

- Rodents are not kept away this way

Many people cover their outdoor compressor units in order to protect them from animals. particularly rodents. Interestingly, covering the unit actually helps the rodents find a warm place to spend their winters at. So they make the inside or downside of the unit their home. The mess they create and the damage they cause is, of course, something you already have an idea about.

- A simple cover is all okay 

While there is no need to fully cover the unit, there is a need to cover it. And that is because, in winter, leaves fall and dust & debris gets accumulated on the unit particularly when it is not operational. So covering it up with a simple cover helps keep dust, debris and leaves away. Also, in case of a storm, other stuff may bang into the unit and get stuck therein when there's no cover at all.
So yes, cover it but the cover shouldn't be a seal.

Bottom line - Outdoor units are durable! 

The parts of the air conditioner that are meant to stay in the outdoor are designed in such a way so as to withstand the toughness of the climate conditions. The latest models, in particular, come with designs that offer special safety to the unit. So there is not really a need to fully cover the unit but even if it is covered, it should be done in such a way so as to leave some space for the unit to breathe in and out. And as said above, a normal fabric cover is well enough to protect the unit from dust, debris and leaves and at the same time, to keep it cool enough so as not to offer a residence to rodents and other animals.
A side tip in order to keep pests and animals away is to use a professional's suggested spray around the unit to keep all these unit corroding elements away.
Do you cover your unit in winters? If yes, how? If not, why not?