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The Model / Serial data label was almost always on the outside of the control box cover on the older comfortmakers. (see picture) I've seen a few high efficiency models where the label is down near the lineset connection on the cabinet. The labels typically peel off or become unreadable after a few years of weathering - If you find that you have a label with no printing on it you can sometimes rub a little dry dirt on it to get the lettering to show up (only slightly and still really hard to read). - Also, most cell phone cameras have better contrast than your eye - I can sometimes take a picture of an unreadable label and I can read it in the photo. - Unfortunately, If the label is missing no amount of dirt will bring it back....
You might have better luck with the compressor model number and serial number - Those are usually on stamped metal plates that don't wear off - The manufacturer (or a distributor) might be able to cross reference those numbers and determine the unit info.
Comfortmaker uses Copeland compressors so the tag is probably on the side of the casing near the bottom - Probably hard to see unless you take the top off and get down between the compressor and the coil