In many cases, one can determine the date of manufacture of an air conditioning unit by means of the serial number. However, different manufacturers encode the dates onto the serial numbers differently.
Manufacturers have particular coding mechanisms in serial numbers that represent the month and year or group of years in which the unit was built. For example, General Electric HVAC units have 11-character serial numbers. The first letter represents the month and the second letter represents a group of years. For example, a "ZT" represents December and the years 2010, 1998, 1986, 1974 or 1960.
Some manufacturers have multiple serial formats. For example, Samsung HVAC units have 10, 14 or 15 alphanumeric characters. In the 10-digit format, the fourth and fifth character represent the year and month respectively. Trane has eight known styles of serial numbers and sometimes lists the date in a separate field.