Johnson Controls is the parent company of York Products

All York products are set up with a systematic coding system for both model numbers and serial numbers. Unit model number (including any dash numbers) and serial number must always be used when referring a problem to York in regard to repair parts, literature, wiring diagrams, etc. Use of proper unit identification numbers and serial numbers will greatly help in expediting any material required for these products.
The sequence of letters and digits in the York model number reflects specific information about the unit. The figures below analyze two typical model numbers.
York Designates the tonnage by digits in the 4th and 5th spaces of the model number.  (I.E. YHE24B21SA)

18 = 1.5 tons
24 = 2 tons
30 = 2.5 tons
36 = 3 tons
42 = 3.5 tons
48 = 4 tons
60 = 5 tons