HS 23 is a model number The rest doesn't make sense. Serial numbers are as follows: first two digits is the plant. Second two are the year made. Letter is the month beginning with A = January. Trane Heat Pump Serial Number Decoder >>>CLICK HEREair conditioner & heat pump inspection, installation, diagnosis & repair article series explains in detail the inspection, troubleshooting diagnosis, and repair. Taylor 6007BG10000D Serial I/O PC Board 6007BG10000-D ABB PCB PLC Trane 02-790858-01 Rev 2 P/L 4.