My air conditionaing unit booklet includes three different reference numbers. They are as follows: 38CKB(N), 38CMB, 38BRB Split-System Air Conditioner. Do the numbers represent the furnace, top floor unit, and bottom floor unit? If so, what number would I use to locate the unit that needs the compressor (top floor)? Also, what is the cost for replacing a 3.5 ton Carrier compressor?