American Blower Company in Detroit

Was inspecting a block house today and it had the coolest double AC unit in the garage. It was made by a company called American Blower out of Detroit.

Had semi-hermetic compressors at both ends of the unit; freon and water lines going to it. Nothing came on so I could not check it in operation. Data tag was worn but for size it said … 3C7-1. Model # was 251-3. S/N was 7B1109-F

Wondering if that means the age is 11th month of 2009 OR 9th month of 2011. Never did peg the size.

What do you guys think?