Q) If I daven in a Shul where the Aron Hakodesh is not on the mizrach side – to which direction should I face while davening?
A) The Shulchan Aruch (OC 94:1) rules that an individual who is in chutz lo’orez should daven facing towards Eretz Yisroel. One who is in Eretz Yisroel should daven facing towards Yerushalayim, and one who is in Yerushalayim should daven facing towards the mokom hamikdosh. [This concept is generally referred to as facing “mizrach“; although the actual direction that one should face when davening is not necessarily due east but will depend on where one is located relative to Eretz Yisroel, Yerushalayim and the mokom hamikdosh.]
The Mishna Berura (Siman 94 s.k. 9) adds that since we are supposed to daven facing mizrach, the minhag is to place the Aron Hakodesh on the eastern side of the Shul[1]. If it is not possible to place the Aron Hakodesh on the eastern side one should place the Aron Hakodesh on the southern side of the Shul; but one should under no circumstances place the Aron Hakodesh on the western side of the Shul because this will cause those who are davening to have their backs towards the Aron Hakodesh. The Mishna Berura concludes that if the Aron Hakodesh was placed on a side other than east, one should still face mizrach while davening [and not towards the Aron Hakodesh].
The Mishna Berura adds (s.k. 10) that if an individual davens in a Shul where the Aron Hakodesh was placed on a side other that east and the tzibbur face the Aron Hakodesh while davening [even though this is not correct practice – as quoted above] the individual should also face the same direction as the tzibbur, but should turn his face towards the east.
[Therefore, when the Mishna Berura earlier (s.k. 9) ruled that one should face mizrach even if the Aron Hakodesh is located on a different side, it appears that he is either discussing an entire tzibbur or an individual who is davening in such a Shul by himself – not with the tzibbur.]
[1] וכן משמע מדברי השו”ע (סי’ ק”נ סע’ ה’)