You need the model, which is displayed on a sticker or data plate, usually on the side panels or behind the filters. Some models may also have an 11 digit Product number (PNC).
Here's What you should See
Your model number may be a combination of letters and numbers and could also include characters such as a dash (-) or a slash (/). If your model has a Product Number (PNC), it will consist of 9 digits followed by a (/) or "space" and ending with a further 2 numbers. Example: 912345678/00 or 912345678 00