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Serial Number format: L943321238 (This serial number is from an actual furnace). Date of Manufacture: Using the second, third, fourth and fifth digits of the serial number L. 21238 you will find the year and week of manufacture. The second and third digits are the year of manufacture and the fourth and fifth digits are the week. Age: Through the 1960s Carrier used the first digit of the serial number to indicate the year of manufacture. Example: 3xxxxx = 1963, 4xxxxx = 1964, 5xxxxx = 1965, etc.
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