Does anyone have a chart for the what the m/n & s/n's mean on all the major brand of furnaces or a/c's. Some mfg make it easy to determine the age of equip and others maker it difficult. I have accumulated a few charts but was wondering if anyone had others. I have Carrier, Trane, & Lennox. I would like York, Luxaire, Comfortmaker, and other common furnaces/air cond. ANy info would be greatly appreciated.