The serial number label is located on the top, right-rear of the outdoor unit. The serial number label is located on the door of your indoor unit. (Your indoor unit is most likely located in your closet, attic, basement or garage.) The serial number label is located on the right or left side of the indoor unit.Click to see full answer. Also asked, how do you read carrier serial numbers?Age: Four digits of serial number indicate date of manufacture where first two indicate the week and the third and fourth are the year. In the 1960s and early ’70s this was the last four digits. More recently date of manufacture information is found closer to the middle of the serial number. how do I read my air conditioner model number? Look at the model number (Located on the data plate stamped on the actual side of the compressor) on the compressor and there should be a number divisible by 12. It should start at 18 and not be more than 60 for residential AC units. 18 to equal 1.5 tons and 60 to equal 5 tons of cooling. Just so, how do I read my first company serial number? The first letter of the serial number denotes the year of manufacture, based on the listing below. The serial number may be noted on two lines, as below, or one line. So the “I” in the serial number above indicates the unit was manufactured in 2001.How do I read my Lennox model number?The model is identified by a “model number” which is stamped on the unit nameplate or rating plate. On residential gas and oil furnaces this identification plate is located on the inside of cabinet near the vestibule panel. On other Lennox products the plate is mounted on the outside of unit.