How old is my air conditioner?

Trane publish a decoder that dates a unit to the day. That is finer than anything else on this site — the guitar and piano pages give a year, or a year block, or a floor. An air conditioner is a warranty item, so the maker needs to know exactly when it left the line, and they put it in the serial number.

Trane publish the scheme, and it is theirs

Trane Technologies publish a serial number decoder as a PDF, free, with a worked example. Go and read it: it will date the unit, and it is the manufacturer saying so.

The field names and their worked example are not reproduced here. Trane's terms restrict commercial use of their content without written permission, and this site is going to carry advertising. Permission to describe the format is being asked for, and the day the answer is yes this comes back — along with the decoder that used to run on it.

Two things this page worked out are worth carrying with you, because they are ours rather than theirs. The first: the day-of-week field stops at Saturday. There are six days in it, not seven, and there is no Sunday — so a decoder that spread 1–7 across Monday to Sunday would invent a production day and mislabel every Saturday unit, with nothing on screen looking wrong.

The second: only half of those days are actually printed. Trane give the first two and the last and elide the middle three, so Wednesday, Thursday and Friday are implied rather than stated. Filling them in is the only sensible reading of a numbered sequence — but it is a reading, not a quotation, and anything that presents it as the manufacturer's word is overstating what the manufacturer wrote.

The week number is where the precision runs out

Trane's own description of that field names a week of the calendar year and never says how they number weeks. That matters more than it sounds, because there are two common conventions and they do not agree:

In some years the two agree. In others they are a week apart, which for a day-level answer means being seven days out. Trane are an American manufacturer, which is a hint and not an answer — so this page shows the date under both and tells you when they differ, rather than quietly picking one and presenting a single confident date.

That is the whole difference between this and a lookup that prints one date. The serial genuinely carries a day. What it does not carry is which of two calendars Trane were counting in.

Which units this covers

The decoder is published under the Oxbox brand — Trane Technologies' value line — and the letter J in the example is what marks an Oxbox unit. Trane, American Standard and Oxbox are the same company's residential equipment, and the serial format is shared. The letter identifies the brand or plant, so a letter other than J is a different line, and the tool reports the letter rather than claiming to know every one.

What we could not get. Trane also publish “How to read a Light Commercial Unit Serial Number Date Code” in their support knowledge base. Their robots.txt permits it, and their server returned HTTP 403 to us anyway. So the light commercial scheme is not here, and we are not going to guess at it from the residential one.

What the other makers publish

The pool is 165 HVAC companies, listed in hvac-makers.txt, taken from Wikipedia's category rather than recalled, with websites from Wikidata's official-website property rather than guessed. Every one with a recorded site was swept, in seven languages.

And read the swept figure knowing how much was there to read. Of the 84 counted as swept, 29 offered this method fewer than 25 pages to look at, and 27 of those offered nothing from a sitemap at all. A host that answers, allows us, and then has almost nothing to search still counts as swept. It is the number of doors opened, not the number of rooms searched.

Of the 28 not probed: 13 did not answer, 5 returned 403 on robots.txt itself so their rules could not be read, 1 disallow us in robots.txt, and the rest were one-off errors. Among those refusing outright or by 403: Panasonic, Hisense, Belimo, Thermax, KMC Controls and Breville. Nothing was taken from any of them.

These figures moved once, and the reason is worth knowing. An earlier version of this table said 79 swept and 33 unreachable. The sweep was re-run with a tighter per-host time budget and a shorter timeout, and five hosts that had previously been given up on answered in time. Nothing about those makers changed — our patience changed. That is what a “could not be reached” figure really measures.

What “nothing found” is not. It means this method found nothing. It missed Rheem on this very page — see the correction below — and it missed Zippo and Ludwig on other pages. Read 79 as swept, not as cleared.

Rheem — month and year, and a typo of their own

Rheem publish their water heating format, and read it for you. Ten characters, carrying a month and a year rather than a day — so a Rheem serial dates an appliance to within a month, which is better than most makers manage.

One thing worth knowing before you go, because it is this page’s own reading rather than theirs, and it is the trap in the format:

Here the century really is ambiguous, and on the date-code page it was not. Zippo and Browning both resolve cleanly because their two-digit years cannot fit both centuries. Rheem have manufactured since 1925, so 25 fits 1925 and 2025, and 26 fits 1926 and 2026. Exactly those two — computed, not assumed — and the tool shows both readings for them.

A correction. An earlier version of this page said Rheem publish nothing readable, because two of their URLs returned navigation and no content and I concluded their pages were JavaScript-gated. A third URL — which our own sweep had already listed — decodes the serial in plain static HTML. The fault was not checking a link we already had.

Building the maker list, and what it nearly got wrong

One Wikipedia category carries this family, which is a relief after band instruments where the saxophone had no category at all. Three things still went wrong, and all three are the kind that produce a confident, wrong list:

• York has no article of its own. “York International” redirects to Johnson Controls, who bought them. The brand is real and the company is not separate — the same problem the piano page has with stencil pianos, where the name on the front is not the name of the maker.
• Rheem was nearly dropped as a disambiguation page. Their article is “Rheem Manufacturing Company”. Elka, Lowrey and Besson were caught the same way on earlier pages.
• Nine entries were not companies at all — four Supreme Court cases, a golf tournament, two stadiums, a concert hall and a labour dispute, all pulled in because the category tree carries anything tagged with a parent company's name.

Filtering that last group by pattern went wrong immediately: matching their categories caught Sanyo (“thin-film cell manufacturers”) and Toshiba (“state-owned film companies”) — two real manufacturers, dropped by a word sitting inside another word. That is the eighth time on this site. They are now removed by name, each with a reason written down.