How old is this rooftop unit?

Reading a Carrier serial number

Ten characters. Positions 1–2 are the week of manufacture on Carrier's fiscal calendar, 3–4 the year, 5 a manufacturing-location letter and 6–10 a sequence number. Carrier's example 3112U12345 was built in week 31 of 2012.

• Positions 1–2: Week of manufacture (fiscal calendar)
• Positions 3–4: Year of manufacture (12 = 2012)
• Position 5: Manufacturing location
• Positions 6–10: Sequence number

Source: 48TC-19PD, page 72.

Applies to: Carrier WeatherMaker 48TC, Carrier WeatherMaker 50TC. Not yet confirmed for Carrier WeatherMaster 48HC, Carrier WeatherMaster 50HC.

Reading a Lennox serial number

A two-digit plant code, a two-digit year, a month letter, then a five- or six-digit sequence number. Lennox’s own example 5178M 99989 came from plant 51 in December 1978.

• Scope: One serial numbering system across Lennox products
• Positions 1–2: Plant (location) code, e.g. 56 = Stuttgart, Arkansas
• Positions 3–4: Year (21 = 2021)
• Position 5: Month letter: A = January, B = February, C = March … M = December (no I)
• Positions 6 onward: Five- or six-digit unique number

Source: Lennox 3.1 Model Numbering Systems, pages 1, 3; Lennox EHB model ID, R-454B and R-32, page 9.

• Lennox’s commercial rooftop handbooks don’t explain the serial. Its current table is in the residential model ID handbook and lists only January to March; its all-products numbering guide shows the same layout in a diagram with every month, A to M without I. We use that month list.
• Plant codes have changed over the years, so we date the unit but don’t name the plant.

Applies to: Lennox Energence LGH/LCH, Lennox Landmark, Lennox Model L LCM, Lennox Model L LGM.

Reading a Rheem serial number

Since November 2013: a plant letter, two digits for the week, two for the year, then a production number. Rheem’s example F 08 13 9999 was built in week 8 of 2013. Older units carry a longer serial whose last part reads the same way: plant F (Fort Smith, Arkansas), week, year, production number.

• Position 1: Plant code
• Positions 2–3: Week of manufacture
• Positions 4–5: Year (13 = 2013)
• Remaining digits: Production number
• Before November 2013: Component codes, then plant F (Fort Smith, AR), week, year and production number
• Plant F: Fort Smith, Arkansas

Source: 92-42800-RKNL-B, page 3.

• Rheem documents the serial in the RKNL-B parts list (6–25 tons, published on Rheem’s parts site). The 3–5 ton and RKPL lists we found show the same pre-2013 layout. We apply both layouts to the whole RKNL/RKPL family; check the date against the rating plate if it looks wrong.
• Rheem doesn’t list the plant letters used since 2013, so we date the unit but don’t name the plant.

Applies to: Rheem / Ruud RKNL and RKPL (R-410A). Not yet confirmed for Rheem Renaissance RGEC / RGED gas/electric.

Reading a Trane serial number

Ten characters on light commercial units built since 2010. Positions 1–2 are the year, 3–4 the week, 5–9 a sequence number and 10 the plant letter: A Monterrey, D Clarksville, L Lynn Haven. Trane’s example 1505 00273 D was built in week 5 of 2015 at Clarksville.

• Positions 1–2: Year, two digits since 2010 (15 = 2015)
• Positions 3–4: Week of manufacture
• Positions 5–9: Sequence number
• Position 10: Plant: A Monterrey, D Clarksville, L Lynn Haven

Source: Trane Support article 44514808922893.

• Trane shows the position layout and plant letters in a diagram in the article; its text names the fields and lists the year codes. We read the positions from the diagram.
• Units built 2002–2009 use a one-digit year and earlier units a year letter. Trane lists those codes but doesn’t show where they sit in older serials, so we only date the ten-character format used since 2010.
• Trane’s year table prints 2019 as “10” and 2025 as “23”. We read both as typing errors: 19 is 2019 and 25 is 2025.

Applies to: Trane Precedent YSC/YHC/TSC/THC, Trane Precedent YSK/YHK/TSK/THK (R-454B), Trane Voyager 12.5–25 ton.

When the serial won’t tell you

• Read the whole nameplate. Some print a manufacture date of their own.
• Call the manufacturer’s technical support or your local rep with the model and serial. They can look up the build record.
• Check the start-up report, the warranty registration and the building’s service records.
• The build date isn’t the install date. Units can sit in a warehouse or on a job site for months before start-up.