Description: Nine (9) character Serial number begins with two (2) numerical digits followed by a single letter digit and ends with six (6) numerical digits. Year of manufacture is the 1st and 2nd numerical digits of the serial number combined. Sep 02, 2010 A quick tutorial on how to locate the serial number on your Friedrich air conditioner. A quick tutorial on how to locate the serial number on your Friedrich air conditioner. Air Conditioner.