How to Read the Date Code on a York HVAC Rating Plate
Quick answer: identify the serial pattern before decoding it
To determine York age by serial number, find the complete serial on the factory rating or data plate, normally near the model number. Identify the serial’s character pattern before decoding the date. Common York formats use different character positions, so applying the wrong rule can produce a plausible but incorrect result.
Use this three-path decision tree:
-
Clear newer-pattern match - The serial is commonly reported as having 10 characters. - Its prefix follows a letter–digit–letter–digit arrangement: positions 1 and 3 are letters, while positions 2 and 4 are digits. - Read positions 2 and 4 together, in that order, for the two-digit year. - Read position 3 for the month code. - Example structure:
W1M7xxxxxx -
Potentially ambiguous legacy match - The serial generally begins with four letters followed by six digits. - Position 2 is the month code. - Position 3 is the year code. - Some year letters repeat on a 21-year cycle, so the serial may produce two possible years. - Example structure:
CETP317723 -
Manual review required - Recheck the transcription and confirm that you copied the equipment serial rather than a model, part, barcode, or accessory number. - Preserve a photograph of the entire rating plate. - Use the model, equipment type, installation records, and manufacturer or dealer assistance to investigate the format.
These are commonly reported third-party decoding rules, not an official York or Johnson Controls serial-number chart. They may not cover every York factory, product line, or historical format. The Building Intelligence Center’s York age guide describes the principal newer and older arrangements but also uses overlapping descriptions for equipment made in 2004.
Treat 2004 as a transition case. Some references describe the newer format as having been used “since 2004,” while others place the change around October 2004 or describe the older format as continuing into that year. Follow the serial’s actual letter-and-digit pattern rather than choosing a rule based on an estimated installation date.
Find the correct rating plate and copy the right number
The serial number is normally printed on the equipment’s factory rating plate or data label, usually near the model number. Look for a field marked Serial No., Serial, or S/N. Do not assume that the largest or most prominent string on the label is the equipment serial.
For an outdoor air conditioner condenser or heat pump, inspect readily accessible exterior areas:
- Both sides of the cabinet
- The back of the unit
- The top or rear label area
- The exterior area near the electrical-access cover
For a furnace or air handler, inspect the cabinet exterior, the front access-door label, and other readily visible manufacturer labels. A label may be attached to the inside face of an ordinary cabinet door.
Safety boundary: Read only labels that are safely accessible. Do not remove an electrical panel, defeat an access control, or reach near energized components merely to find a model or serial number. If the label cannot be viewed safely, ask qualified service personnel to identify it. Third-party equipment-age guidance gives the same warning and notes that indoor and outdoor components may have different identifiers and ages (Beacon HVAC Age Finder).
Serial number versus other identifiers
A rating plate may contain several similar-looking numbers. Record the value specifically labeled as the serial number.
Do not substitute:
- The model number, which identifies the equipment family and configuration
- A barcode number that is not labeled as the serial
- A replacement-part or control-board number
- A manufacturing part number
- An accessory-kit serial
- The serial of a replacement motor, coil, control, or other component
Photograph the entire rating plate before transcribing anything. A full photograph preserves the model, brand, equipment type, certification information, electrical data, label design, and surrounding text. Those details may help distinguish between possible legacy years or reveal that the selected label belongs to a replacement component.
Keep spaces, parentheses, hyphens, and punctuation visible in the photograph. You may normalize the serial for analysis later, but retain the original presentation. A parenthesized leading letter in some older serials may be excluded when positions are counted; deleting it from the original record can obscure why the positions appear to shift.
Remember that an HVAC “system” can contain several independently manufactured units. The outdoor condenser or heat pump, indoor furnace, air handler, evaporator coil, and packaged accessories can each have their own data plate. They may have been manufactured or replaced at different times, so check each component independently.
Before decoding, complete this checklist:
- [ ] York is the brand named on this equipment label.
- [ ] I recorded the complete serial number.
- [ ] I recorded the complete model number.
- [ ] I identified whether this is a condenser, heat pump, furnace, air handler, coil, or packaged unit.
- [ ] I photographed the entire rating plate.
- [ ] I compared my typed serial against the photograph twice.
- [ ] I did not copy a barcode, part number, or accessory identifier.
Decode the commonly reported newer York format
The commonly reported newer format is a 10-character serial whose opening characters follow a letter–digit–letter–digit arrangement:
| Position | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|
| Example | W | 1 | M | 7 | 3 | 1 | 7 | 7 | 2 | 3 |
| Reported function | Plant or location | Year digit | Month | Year digit | Sequence | Sequence | Sequence | Sequence | Sequence | Sequence |
Using W1M7317723:
- Position 2 is
1. - Position 4 is
7. - Read those characters together, in that order:
17. - Position 3 is
M. - In the reported newer month table,
Mmeans November. - The example is therefore reported as November 2017.
The first character is described as a manufacturing-plant code and is not part of the date calculation. The Inspector Handbook York decoder uses this example and reports November 2017.
Newer-format month codes
For a serial that clearly matches the newer arrangement, the reported month codes are:
| Code | Month |
|---|---|
| A | January |
| B | February |
| C | March |
| D | April |
| E | May |
| F | June |
| G | July |
| H | August |
| K | September |
| L | October |
| M | November |
| N | December |
Notice that the sequence omits I and J. Do not count alphabetically from January; use the reported table.
A second example is W1G7123456:
| Date position | Character | Meaning |
|---|---|---|
| 2 | 1 |
First year digit |
| 3 | G |
July |
| 4 | 7 |
Second year digit |
Positions 2 and 4 form 17, and G represents July, producing a reported manufacture date of July 2017. Parts Town supplies both the newer month mapping and this worked example in its York serial-number guide.
You may also encounter W1D5 as a prefix-only illustration. Under the reported rule, positions 2 and 4 form 15, so the prefix has been described as indicating 2015. The supplied explanation does not independently establish the month, so this prefix should not be treated as a complete month-and-year example.
Do not overlook the century question
The rule produces a two-digit year, not an independently verified century. In a modern equipment context, 17 may reasonably indicate 2017, but the serial characters do not literally state “2017.”
If the century is genuinely uncertain, examine:
- Equipment type and model family
- Rating-plate design
- Certification or industry-standard references
- Original property records
- Installation and service documentation
- Whether the cabinet and original components are consistent with the proposed era
Record an unresolved century as unresolved. Do not automatically convert every 17 to 2017 merely because the prefix matches the newer arrangement.
Treat this as a commonly reported format associated with the period beginning around October 2004, not a guarantee that every later York-branded product uses it. An unexpected serial length, extra prefix, different product category, or conflict with the full label calls for manual verification.
Decode the older four-letter York format
The commonly reported older structure generally consists of four letters followed by six sequence digits:
| Position | 1 | 2 | 3 | 4 | 5–10 |
|---|---|---|---|---|---|
| Typical character | Letter | Letter | Letter | Letter | Six digits |
| Reported function | Manufacturing location | Month | Year | Unit type | Sequence |
Under this method, the date calculation uses:
- Position 2 for the month
- Position 3 for the year
Positions 1 and 4 may describe manufacturing or equipment information, but they do not supply the date.
Older month codes: incomplete table
The third-party legacy table supports these month codes:
| Code | Month |
|---|---|
| A | January |
| B | February |
| C | March |
| D | April |
| E | May |
| F | June |
| G | July |
| H | August |
| K | September |
| L | October |
| M | November |
This table is intentionally incomplete. The available legacy evidence does not reliably establish a December code for every older York format. Do not infer that December must be N merely because N represents December in the newer system. The legacy month list and its limitation appear in the Parts Town guide.
Older year codes and the repeating cycle
The reported legacy year sequence includes numerous letters that may correspond to either of two years:
| Code | Reported year or years |
|---|---|
| A | 1971 or 1992 |
| B | 1972 or 1993 |
| C | 1973 or 1994 |
| D | 1974 or 1995 |
| E | 1975 or 1996 |
| F | 1976 or 1997 |
| G | 1977 or 1998 |
| H | 1978 or 1999 |
| J | 1979 or 2000 |
| K | 1980 or 2001 |
| L | 1981 or 2002 |
| M | 1982 or 2003 |
| N | 1983 or 2004 |
| P | 1984 |
| R | 1985 |
| S | 1986 |
| T | 1987 |
| V | 1988 |
| W | 1989 |
| X | 1990 |
This mapping is reported by a home-inspection reference on York equipment age, which says the letter series repeated on a 21-year cycle. That is why several codes do not identify a unique year.
No definitive Y mapping is included here. One supplied third-party table assigns 1992 to both A and Y, creating an internal inconsistency. Rather than guessing at a correction, this guide leaves Y unresolved.
These mappings remain third-party interpretations. Their inclusion does not make them official York codes or establish that every legacy product follows the table.
Example: CETP317723
Number the characters:
| Position | 1 | 2 | 3 | 4 | 5–10 |
|---|---|---|---|---|---|
| Character | C | E | T | P | 317723 |
- Position 2 is
E, reported as May. - Position 3 is
T, reported as 1987. - The resulting manufacture date is May 1987 under this legacy mapping.
The initial C and fourth-position P do not supply the date under this method. Inspector Handbook demonstrates this specific serial and result in its York legacy decoder.
Example: WDHP875237
Number the opening characters:
| Position | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| Character | W | D | H | P |
Here, D occupies the month position and represents April in the reported table. The year code is H, which can represent 1978 or 1999. The supported result is therefore:
April 1978 or April 1999—manual confirmation needed.
The serial does not authorize choosing 1999 merely because it appears more likely. The worked ambiguity and repeating year mapping are described in the cited home-inspection reference.
Parenthesized leading characters
A serial may appear as:
(S)EBHM062202
For this reported variation, ignore the parenthesized S when numbering the underlying legacy serial. Start with E as position 1, B as position 2, H as position 3, and M as position 4. The Building Intelligence Center guide specifically describes this treatment for its (S)EBHM062202 example.
Do not delete the parenthesized character from your original notes. Preserve the complete printed serial in the rating-plate photograph, then state separately that the parenthesized character was excluded from position counting under the reported legacy rule.
Resolve a 2004 transition date or an ambiguous legacy year
The third-party sources do not describe the 2004 boundary identically. Some call the newer style a format used since 2004. Others say the older style ran through approximately October 2004 and the newer style began around that time. Another describes one style as “2004 onward” while also labeling the other “2004 and prior.”
That disagreement makes a pattern-first approach essential.
For equipment believed to date from 2004, do not begin with the installation estimate. Begin with the serial:
- Four letters followed by six digits: investigate it as a legacy pattern.
- Letter–digit–letter–digit prefix: investigate it as the newer pattern.
- Anything else: do not force it into either table.
A supposed installation year is not enough because manufacture can precede installation. A homeowner’s recollection, real-estate listing, or handwritten service note may also refer to a repair or component replacement rather than the installation of the unit being examined.
Checklist for resolving two possible legacy years
When a repeating code produces two years, use the complete context:
-
Full rating plate Look for surrounding dates, label style, certification marks, referenced standards, electrical information, and equipment descriptions.
-
Model context Determine whether the model family is consistent with one proposed era. Treat the model as supporting context rather than decoding it with an unrelated model-number rule.
-
Certification or standard dates A standard dated after one proposed manufacturing year may eliminate that earlier possibility, provided the reference is interpreted correctly.
-
Physical design Cabinet construction, controls, connectors, labeling, and apparently original components may be consistent with an era. Use caution because individual parts can be replaced.
-
Physical condition Corrosion, paint, weathering, and wear can provide context but are not proof. A protected and well-maintained older unit may look relatively new, while harsh conditions can make a newer unit look much older.
-
Property history Compare the candidate years with the building date, additions, major renovations, and documented ownership history.
-
Permits and inspections Local records may identify an HVAC installation or replacement associated with the property.
-
Invoices and service records Installation invoices, equipment schedules, maintenance stickers, and prior service reports can connect a model and serial to a date.
-
Manufacturer or dealer review Provide the full label photograph—not only the typed serial—to York, Johnson Controls, or an authorized York dealer.
For WDHP875237, the H year code permits 1978 or 1999 under the reported table. If reliable records show that the relevant portion of the house was built in the late 1990s and that the equipment was installed during that construction, the records may support 1999. Without such evidence, the appropriate result remains “1978 or 1999—manual confirmation needed.”
Apply the same discipline when a newer-format serial gives a two-digit year whose century is unclear. A letter–digit–letter–digit match identifies the positions used by the reported rule, but it cannot replace contextual evidence where more than one century remains plausible.
Before using a decoded date in a property transaction, warranty dispute, insurance matter, or major repair-versus-replacement decision, seek confirmation through reliable installation records, York, Johnson Controls, or an authorized York dealer. A third-party decoding table can support an estimate, but it is not manufacturer verification.
Calculate the unit’s manufacturing age correctly
Manufacturing age is the elapsed time from the decoded manufacture month and year to a stated calculation date. Because the examples establish only month-level precision, describe the result as an approximate calendar age.
Use this method:
- Subtract the manufacture year from the calculation year.
- If the manufacture month has not yet occurred in the calculation year, subtract one from the whole-year result.
- Count the remaining months if month-level detail is useful.
- State the date on which the age was calculated.
For example, W1M7317723 is reported as November 2017 under the newer rule. As of August 2026, November 2025 is the last anniversary month reached. The unit is therefore approximately 8 years and 9 months past its manufacturing month.
A record could read:
Reported manufacture date: November 2017 Manufacturing age as of August 2026: Approximately 8 years, 9 months
Avoid writing only “the unit is 8 years old.” Without an as-of date, that statement becomes stale and discards the month information available from the code.
Manufacturing age is not time in service
Manufacture date and installation date are separate. Equipment can remain in inventory before installation, so its manufacturing age can exceed its actual time in service. Third-party HVAC age guidance also explains that indoor and outdoor components can have different dates and that estimated age does not determine warranty status (Beacon HVAC Age Finder).
Keep these fields separate whenever possible:
- Manufacture month and year: Decoded from the equipment serial
- Installation or commissioning date: Established by an invoice, permit, registration, or other record
- Time in service: Elapsed time since installation
- Manufacturing age: Elapsed time since manufacture
Serial decoding does not establish warranty status. Coverage may depend on installation date, registration, the covered part, transfer provisions, and manufacturer records. Do not state that a unit is in or out of warranty solely because its serial suggests a particular manufacturing date.
Age alone also does not establish:
- Current condition
- Maintenance history
- Operating efficiency
- Safety
- Code compliance
- Remaining service life
- Whether a repair is economical
- Whether replacement is appropriate
A decoded date is one fact about the equipment. It is not a diagnosis or a replacement recommendation.
Troubleshoot a serial number that does not fit either pattern
If the serial will not decode, investigate transcription and identification problems before concluding that the equipment has no usable date code.
1. Recheck look-alike characters
Compare the photograph carefully for characters that are easy to confuse:
0andO1andI5andS8andB
Inspect faded areas for an omitted character. Count the complete string rather than relying on where a stain, scratch, or smudge appears to divide it. Adjusting the contrast on a copy of the photograph may help, but retain the unedited original.
2. Confirm that it is the equipment serial
Verify that the value is explicitly marked Serial No., Serial, or S/N. A model number, barcode, control-board number, replacement part, or accessory-kit serial will not necessarily follow the complete unit’s date pattern.
If several labels are present, identify which one is the manufacturer’s rating plate for the equipment being dated. Replacement components may carry newer labels that do not represent the cabinet’s manufacture date.
3. Restore the original punctuation
Check whether a space, hyphen, prefix, suffix, or parenthesized letter has shifted the apparent positions. For an older serial printed like (S)EBHM062202, the reported method excludes the parenthesized S when numbering the underlying serial.
That is a documented treatment for a specific legacy variation, not permission to discard arbitrary characters from an unrecognized serial.
4. Confirm the component
A condenser, heat pump, furnace, air handler, evaporator coil, and replacement component can each carry a different identifier. Make sure the label belongs to the exact component whose age you are trying to determine.
A newer outdoor condenser does not establish the date of the indoor furnace. Likewise, a recently replaced control board says nothing conclusive about the manufacture date of the complete unit.
5. Preserve the evidence for manual review
Keep a clear photograph showing:
- The complete rating plate
- Brand
- Model
- Serial
- Equipment type
- All prefixes and punctuation
- Nearby certification or standard references
- The cabinet area where the label was found
A typed serial by itself makes it difficult for a dealer or manufacturer representative to detect omitted characters or identify the product family.
6. Treat online lookup output as an estimate
Some third-party tools accept York as a brand and attempt to return a likely manufacturing date. Their output can be useful as a cross-check, but it should not be presented as manufacturer verified.
A tool may list York alongside related or sister brands. That does not prove that every listed brand, factory, era, and product line uses identical serial rules.
One lookup service allows users to submit a label photograph, model, and serial and notes that formats vary by brand (HVACchecker serial lookup). If its result conflicts with the visible serial pattern or complete rating plate, preserve the conflict and escalate it rather than selecting the preferred answer.
Use this escalation order:
- Recheck the label and transcription.
- Compare the serial with the two commonly reported York patterns.
- Review installation, permit, invoice, and service records.
- Ask an authorized York dealer to review the complete rating plate.
- Seek confirmation from York or Johnson Controls.
Continue to follow the cited safety boundary: if reading the label would require opening an electrical compartment or approaching energized components, stop and defer to qualified service personnel.
Record the result without overstating what it proves
A useful written result separates what was observed, what was decoded, and how confident the conclusion is.
Use this template:
Equipment type: Model number: Serial number as printed: Reported serial pattern: Newer / Legacy / Unrecognized Decoded manufacture month and year: Manufacturing age as of: Confidence level: Verification source: Rating plate / Records / Dealer / York or Johnson Controls Notes or unresolved issues:
Use one of these confidence categories:
-
Clear match to a commonly reported newer pattern The complete serial follows the expected letter–digit–letter–digit prefix, its date positions produce a valid reported month and two-digit year, and the label context does not conflict with the result.
-
Legacy match with one contextually supported year The serial follows the four-letter-plus-six-digit structure, the cited legacy mapping supports the proposed year, and available contextual evidence is consistent with it. This category does not mean York has officially verified the date.
-
Ambiguous or unrecognized—manual confirmation required The legacy code produces two possible years, the newer year leaves the century uncertain, the serial does not fit either pattern, or surrounding evidence conflicts with the decode.
Document indoor and outdoor equipment on separate lines:
| Component | Model | Serial | Reported manufacture date | Confidence |
|---|---|---|---|---|
| Outdoor heat pump | Record from label | Record from label | July 2017 | Clear newer-pattern match |
| Indoor air handler | Record from label | Record from label | 1978 or 1999 | Manual confirmation required |
This prevents a mixed-age system from being represented as though all components were manufactured together.
A serial decode supports only an estimated or reported manufacturing date under commonly reported third-party rules. It does not prove the installation date, warranty eligibility, maintenance history, current condition, efficiency, safety, code compliance, or remaining useful life.
Keep the entire rating-plate photograph with the written result. Attach any invoice, permit, registration record, equipment schedule, or service report used to resolve an ambiguous year. If a later reviewer reaches a different conclusion, the underlying evidence will remain available.
No official York or Johnson Controls serial-number chart was supplied for this guide. Unrecognized or conflicting formats should remain unresolved rather than being forced into a date.
Frequently asked questions
Which characters show the year in a newer York serial number?
For the commonly reported newer pattern, positions 2 and 4 are read together, in that order, to create the two-digit manufacture year. Position 3 supplies the month.
In W1M7317723, position 2 is 1, position 4 is 7, and the resulting year digits are 17. As shown in the cited newer-format walkthrough, M is reported as November, giving November 2017 in the example’s modern equipment context.
Apply this method only when the complete serial clearly matches the newer pattern. Because it produces a two-digit year, equipment context may still be necessary when the century is uncertain.
Why does an older York serial number give me two possible years?
The legacy letter series is reported to repeat on a 21-year cycle. As a result, some letters in the third position correspond to two possible years. For example, the cited legacy table maps H to 1978 or 1999.
Use the entire rating plate, model context, standards references, property history, permits, invoices, and service records to investigate. If those clues do not resolve the cycle, report both possibilities and mark the result for manual confirmation.
How should I decode a York unit manufactured during 2004?
Treat 2004 as a transition period because third-party descriptions disagree about whether the boundary was simply “2004,” extended into 2004, or occurred around October 2004.
Follow the serial pattern rather than the presumed installation year. Four opening letters generally point toward the legacy method; a letter–digit–letter–digit prefix generally points toward the newer method. If the pattern is unclear—or the result will affect a consequential decision—obtain confirmation from York, Johnson Controls, or an authorized dealer.
Is the manufacture date the same as the installation date or warranty start date?
No. Equipment can remain in inventory before installation, so the manufacture date may precede the installation or commissioning date.
Serial decoding also does not establish the warranty start date or current coverage. Warranty status may depend on installation documentation, registration, the part involved, transfer terms, and manufacturer records. Keep manufacture date, installation date, time in service, and warranty status as separate fields.
Should I check the indoor and outdoor York units separately?
Yes. Indoor and outdoor components are separate pieces of equipment and can have different models, serial numbers, and manufacturing dates. A system may contain an older furnace or air handler paired with a newer condenser or heat pump.
Photograph each rating plate and record each result separately. Do not apply the outdoor unit’s decoded date to the indoor equipment—or vice versa.
Three-step recap: Photograph the entire rating plate, identify the serial by its character pattern, and decode only the positions supported for that pattern. A clear newer-format match can often produce a month and two-digit year, while a legacy serial may leave two possible years. Label the result as manufacturing age, check indoor and outdoor equipment separately, and seek York or authorized-dealer confirmation when the format is unusual, the 2004 transition is involved, or the date will affect an important decision.