OK how do I search for a very old system? I have the model number and the serial number, but when I go to the mfr website I get no results. I do believe the date of mfr was July 1978 based on s/n, but can't seem to find anything else out about it, especially the SEER rating, (Which is the challenge I was given)....Any old timers can help out this 62 y/o newbie?