I have a Carrier 38YR018320 installed with an air handler FK4BNF001 in 1994. Since I have no documentation on the unit, I have been searching the web and found that an 018-30 series matched with that air handler has a TDR-TXV (the outside unit label mentions a TXV) and is rated at 18,000 BTU and 11.05 SEER. However mine is a 018-32. Can anyone tell me what that last digit after the '3' implies? Thanks again.