window air conditioners

If you mean totaly enclose the usually exposed portion that is outside your home, then the answer is possibly.
If the enclosure is totally enclosed the fins that radiate heat from the compressor will not be able to shed heat efficiently thus rendering your aircon ineffective at best. At worst residual heat will load the compressor to a point where it breaks down.
It may be suitable to enclose your aircon in latice or an open wrought iron structureh however any structure will impede airflow over the fins and reuce effectivness.