ToftThis covers Heil, Tempstar, Comfortmaker, Arcoaire, KeepRite, Airquest, International Comfort Products, Lincoln. The serial number is on the rating plate, usually on the outside of the cabinet.
A letter, then nine or ten digits. The two digits after the letter are the year and the next two are the week of the year.
Example: L004112345 was made in week 41 of 2000.
This is the date the unit was made. It was usually installed soon after, but it can be later. If a serial doesn’t fit any of these patterns, look on the label for a printed manufacture date.
Checked in October 2026.
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