The following will explain a Carrier serial number sequence.
NNNNANNNNN This serial number format was used in the 1970’s through current. The first 4 numeric characters are the week and year of production. For example, a unit that came off the line on March 25, 1999 would begin with 1399, week 13 of the year 1999.
ANNNNNN This serial number was used from 1969 to 1990. The first alpha character is for the month of production.
A-M = Jan-Dec 1969-1979
N-Z = Jan-Dec 1980-1990
‘I’ and ‘O’ are not used
The second digit, a numeric character is the production year
The balance of the numeric characters are the production sequence
e.g., A912345…this serial number would be a unit produced in Jan 1969
P512345…this unit would have been produced in Feb 1985