York, a Johnson Controls brand, has used two different serial-number date formats since 1971, and reading the wrong one produces a wrong decade, not just a wrong year. On the format used from October 2004 to the present, the serial opens with a letter for the manufacturing plant, then a digit, then a second letter, then a digit; the second letter stands for the month, from A for January through N for December, skipping I and J, and the two digits read together give the two-digit year.
A serial opening W1G7 was therefore built in July of 2017 at York's Wichita plant. On the earlier 1971-to-2004 format, the second and fourth characters are both numbers and combine to give the year, while a different letter position carries the month using the same letter table. Independent HVAC-trade and technician references converge on both readings; this site could not locate a current consumer-facing York page stating either rule directly.
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Decode your own serial number
What this covers
- York residential furnaces, air conditioners and heat pumps built from October 2004 to the present, using a letter-digit-letter-digit-plus-six-digit serial
- York equipment built 1971 through September 2004, using an all-letter-then-numeric serial read by a different position rule
- Reading the month from a specific letter position and the year from specific numeric positions, per era
What it does not cover
- ×York equipment older than 1971, which is not covered by either documented format here
- ×A guarantee that every plant-code letter is current — Johnson Controls has added and retired York manufacturing plants over the decades
- ×Luxaire, Coleman or other Johnson Controls-family brands not confirmed to share York's exact layout
Try in this order
0 of 4 completedLocate the rating plate
ReversibleCheck inside the front access panel of a furnace, or the exterior panel of an outdoor condenser or heat pump.
Identify which era the serial belongs to
ReversibleThe October 2004–present format mixes single digits between letters (letter, digit, letter, digit, then six more digits). The 1971–2004 format opens with four letters before any numbers.
Decode the current format (Oct. 2004–present)
ReversibleThe second letter (the third character overall) is the month, A through N skipping I and J. The two numeric digits, read together, are the two-digit year. W1G7 reads as July 2017.
Decode the older format (1971–Sept. 2004) with care
ReversibleThe second letter is the month using the same table; the third letter gives the year, but that letter code repeats every 21 years, so a single letter alone cannot distinguish, for example, 1971 from 1992 without other context such as the equipment's known installation era.
Evidence ledger
Sources behind this answer
Where the manufacturer's article stops. No current York or Johnson Controls consumer-facing page stating either decode rule directly could be located during this review. Both readings below come from independent, mutually consistent HVAC-trade and technician references rather than directly quoted manufacturer text, which is why the evidence grade is B rather than A.
A working HVAC technician's reference confirming York changed formats and that the current format shows the year more directly than the older, letter-only format. Verified Sept. 10, 2026.
Independent HVAC-trade reference giving the exact character-position tables used below for both the October 2004–present format and the 1971–September 2004 format, including the shared month-letter code and both eras' plant-code letters. Verified Sept. 10, 2026.
Exact questions
Questions about Decode a York serial number
How do I tell which of York's two serial formats my unit uses?+
The current format (October 2004 onward) mixes single digits between letters. The older format opens with four letters in a row before any numbers appear.
Why can't the older York format alone confirm the exact decade?+
Its year letter code repeats every 21 years, so the letter alone is ambiguous — for example, the same letter can mean 1971 or 1992. Use another clue, such as the home's known equipment-replacement history, to pick the right cycle.
Is this decode rule published directly by York or Johnson Controls?+
No current York consumer-facing page stating either rule directly could be located during this review. Both readings are mutually consistent trade and technician references, which is why this page is graded B rather than A.
Where do I find the York unit serial number?+
Look for the rating plate or label on the unit, on the unit's data plate. Photograph it before you start, since the label can be hard to read once the appliance is installed.