First I want to thank Sean Leonard for this question.

Covering your outdoor unit seems like a logical thing to do, and we have all seen them outside of someone’s home, and many of us cover less expensive items that are exposed to the elements over the winter.

There are pros and cons to both sides, many contractors may recommend something different. 

PROS TO COVERING YOUR AIR CONDITIONER

  • Prevents heavy debris like sticks, branches, and other yard waste from blowing into your AC unit.
  • Helps prevent water from directly resting on your coils and freezing, which could be damaging. (I have never seen this occur, but it was listed on a couple sites so in rare instances I guess it is something that could happen)

CONS TO COVERING YOUR AIR CONDITIONER

  • Covering an entire unit may actually trap moisture by creating a high humidity environment as the sun beats down on the cover.  Inside this moist environment are your electrical windings, wiring connections, and in some cases circuit boards.  None of these items do well in the moisture.
  • During the winter months, the temperatures cause small animals to find a warm place to nest away from the elements.  A cover can provide a very tempting spot for these animals to call home.  These critters can wreak havoc on your unit by chewing the wiring for their nests.  This can lead to very expensive repairs for you in the spring.

OUR RECOMMENDATION

Covering the unit is not necessary. If you do still want to cover your unit to keep out debris we have found that a simple piece of plywood across the top works nicely.  It is inexpensive and will keep out most debris, but lets the sides open to keep moisture and animals out.