Your question has produced a somewhat complex answer that includes more questions. First, what is an uninsulated “beer shed”, how large is it and can it be insulated? Is it large enough to support the weight of a small window ac unit? I assume the beer shed is an indoor structure whereby the condensing section of the window ac unit will also be indoors? If this is the case, what is the average ambient temperature of the area in which the condensing section will sit and how large is the area, i.e, basement, small closet, etc.. Will heat be needed and how will you introduce heat to this beer shed?
The simple answer to your question is: Yes, it can be done. However, is it a sound economical solution to creating a fermentation chamber? Answers to the above questions will help answer this question.