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How old is my Guardian unit?

Guardian is part of Bosch Home Comfort (ex JCI / York). 2 serial formats sourced across central air conditioner, heat pump, furnace.

Serial number decoder for Guardian

Serial no.

Type the serial from the data plate, not the model number. Nothing is sent anywhere; the tables are in this page.

Format example: W0K5896070

Guardian air conditioner serial numbers in the 2004 to present format encode the year as digit 2 + digit 4 concatenated (0+5 = 2005) and the month as letter 3 (table below) (source: building-center.org).
Example: serial W0K5896070 decodes to September 2005.
Guardian air conditioner serial numbers in the 1971 to 2004 format encode the year as letter 3 via 21-letter table (table below) and the month as letter 2 (A-N, I/J skipped like style 1) (source: building-center.org).
Example: serial WAKM011379 decodes to 1980 or 2001 (January).
The 1971 to 2004 format is ambiguous: Letters A-N repeat (1971-1984 vs 1992-2004): 21-year cycle. Some serials carry a parenthesized leading letter e.g. (S)EBHM062202 - ignore it. Style ran to Oct 2004, so 2004 has BOTH styles.

Decoder pages by product

2004 to present VERIFIED
A#A#######Central Air Conditioner, Heat Pump, Furnace, Packaged Unit
1971 to 2004 VERIFIED
AAAA######Central Air Conditioner, Heat Pump, Furnace

Official lookup: the authority

Open the official York lookup takes serial; returns warranty details ('HVAC WARRANTY LOOKUP'); URL partial

This site is a reference built from published tables. The manufacturer's own lookup wins whenever the two disagree.

No official online lookup URL was verified for Guardian.
Only the York 2004+ style is listed (W0F7982700 = June 2007, Wichita). Discontinued sub-brand; use York's lookup https://york.bosch-hcgroup.com/residential-equipment/warranty-and-registration (200).