The location of model number information for airconditioners can vary greatly upon manufacturer, model and type of system. There are three main types of airconditioner systems:

Ducted Systems will consist usually of two separate units. One located outside of the house/building, the other inside the roof cavity. The outside or 'outdoor unit' will normally have a sticker with the model information located on the side. Sometimes though it may be on the back, which could be difficult to read without a mirror if it is closely located to a wall. The inside or 'indoor unit' being in the roof cavity may be difficult for most people to get to. It will also have a sticker with model information on it. Depending on the manufacturer/model it may be possible to cross reference the indoor unit information from the outdoor model number.

Split/Cassette Systems are very similar to ducted systems, but the indoor unit should be visible either on a wall (known as split system) or in the ceiling (known as cassette system). Outdoor unit information should again be on a sticker located on the side or back of the unit. For split system types, the model number is most commonly located on the bottom edge or side of the unit. Cassette units will most likely be located on the panel behind the filter cover/holder. Make sure the unit is not operating while you remove the cover, and check your owners manual if you are unsure of how to remove it.

Window/Wall Systems will most often contain model number information located on the side of the unit. Unfortunately some installers aren't aware of this, and quite often is the case that it gets covered by the wall.