Where to Find the Serial Number on an AC Unit
The serial number that dates your air conditioner is on the rating plate of the outdoor unit, usually on a side panel near the electrical connections. The indoor coil and air handler have their own.
By Suraj Jha · Updated 2026-11-02
The outdoor unit (condenser or heat pump)
Walk around the outdoor unit and look for a rectangular plate or sticker, typically:
- on the side panel where the copper refrigerant lines and electrical conduit enter, often near the service valves;
- sometimes on the back panel facing the house, which can mean reaching behind it carefully;
- on some brands, on the top panel or inside the electrical access cover.
Don’t remove the electrical access panel to look for a label unless the power is switched off at the outdoor disconnect. There’s high voltage inside.
Inside the house: coil and air handler
| Component | Where it is | Where the label is |
|---|---|---|
| Evaporator coil | On top of (or below) the furnace, in a sheet-metal box | On the coil cabinet, often on the side with the refrigerant connections |
| Air handler | In a closet, attic or garage, used with heat pumps or electric heat | On the side of the cabinet or behind the access panel |
| Ductless indoor head | On the wall | Under the front cover or on the side of the unit |
These carry their own serial numbers and dates. They’re useful when you want to know whether the indoor coil was replaced along with the outdoor unit, which matters for efficiency and warranty.
Model number vs serial number
On the same plate you’ll see both:
- Model number (M/N): identifies the product line and size, for example
24ACC636A003orGSX140361. It shows the capacity. Our AC tonnage finder reads it. - Serial number (S/N): identifies the individual unit and encodes the manufacture date. Our HVAC age lookup reads it.
Reading the age
Brands encode the date differently: some as week and year, some as year and month, some with letters. A few examples:
| Brand | Example serial | Built |
|---|---|---|
| Carrier | 2406E12345 | Week 24 of 2006 |
| Goodman | 0601123456 | January 2006 |
| Trane | 11241ABCDE | Week 24 of 2011 |
| Lennox | 5806K12345 | October 2006 |
| York | W1G7123456 | July 2017 |
Many newer plates also print the manufacture date directly, often labeled MFD, MFG DATE or with a month/year near the bottom. If yours has one, that’s the answer.
While you’re at the plate
- Refrigerant: look for R-22, R-410A, R-454B or R-32. An R-22 system was almost certainly built before 2010. See our R-22 guide.
- Electrical ratings: the minimum circuit ampacity and maximum fuse size are useful if you ever replace the disconnect or breaker.
- Photograph it. A clear photo of the plate saves another trip around the house when you call for service or a quote.
Frequently asked questions
Where is the serial number on an outdoor AC unit?
On the rating plate, a metal plate or printed sticker on one of the side panels, usually the one covering the electrical connections where the power and refrigerant lines come in.
Do the indoor and outdoor units have the same serial number?
No. Each component (outdoor unit, indoor coil, furnace or air handler) has its own serial number and its own manufacture date. They may have been installed at different times.
Which serial number tells me the age of my AC?
The outdoor unit's. It contains the compressor, the most expensive part and the one that decides the system's life.
The plate is faded by the sun. What now?
Photograph it at an angle, with the flash off, and boost the contrast. Check the other side panels for a second label, and look for the model and serial on installation or warranty paperwork.
Next steps
Look up the age of your furnace and air conditioner
More about air conditioners and heat pumps
Browse all guides.