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There should be a metal plate (older models) or a sticker on the machine. This will give the BTUs that the air conditioner is rated at.
If the information is not there then, post the model number from the machine and we should be able to find out the BTU rating is. It should state "model number" or "Mod." or something that will let you know.
Let me know what you find.
What kind of AC is this and where was in installed? Window... Thru the wall... Central air outside?
If it's a room AC and it was working ok before. How large was the room?
The s/n number would be the serial number. So, the first number is XXXXX model number.
I would read that number as the BTUs. So, approximately 22,500 to 23,400 BTUs. Not quite 2 tons.
Ok... I just found comfirmation -- roll down after you download this pdf file and you'll see your model number it is 22,500 BTUs.
Let me know if you need any more information.