This is what I assume is a simple question but one that I can't find an answer to. Why does the deacon unfasten the orarion and cross it over his chest and back during the Lords Prayer?
Such crossing only occurs during Holy Communion. From St. Tikhon's site
Whereas the Sub-Deacon always wears his Orarion crossed, the Deacon, for the most part, wears his on his left shoulder, only crossing them at the time of the Communion of the clergy and the faithful. The Orarion is the Deacon's principal vestment, without which he cannot serve at any service whatever. In ancient times Deacons used to wipe the lips of communicants after they had partaken of the Holy Gifts.
In addition to the Orarion, the Deacon also wears the Cuffs (as do the Priests and Bishops) for convenience during services and also to remind him that he must not put his trust in his own strength alone, but in the right hand of the Almighty God