Rheem & Rudd: in the middle of the serial number will be a letter "F" the following four numbers are the week and year.

Carrier, Bryant, Payne, Day & Night: Recently (last 20 years or so) the first four numbers in the serial number represent the week and year. Previously, it was a complex series of letters and single digits. Call 905 672-0860 if you get stuck.

Lennox: Either the first two or second two digits are the year, it varies by era, but most of them actually have a separate sticker somewhere that has the year printed on it. Newer ones are first two equals manufacturing plant #, 2nd two are year and letter in fifth slot is month (A thru M minus I). So 5898G 07568 would be Plant # 58, Year of MFR would be 98 and month would be July.

Amana: BLACKHORSE. B=1971 or 1981. (Of course, now that they've been bought by Goodman, who knows what'll happen.)

Goodman: First two digits of the serial number are the year. Second two are the month.
Btu rating is model number..ie; GMP075-3 (75,000 bonnet input)
Compressor is same :serial # 9709088872 (yr1997 wk 09) Tonnage is model # CK361C The first two numbers after the CK (letters) divided by 12 is tons. ie: 36 div by 12= 3 tons.


YORK HVAC DATING (Unitary Products since 1984)
Note: they skip the letters I, O, Q, U, Z.
Year of make indicated by 3rd letter in the serial number.

1971 - A 1992 - A
1972 - B 1993 - B
1973 - C 1994 - C
1974 - D 1995 - D
1975 - E 1996 - E
1976 - F 1997 - F
1977 - G 1998 - G
1978 - H 1999 - H
1979 - J 2000 - J
1980 - K 2001 - K
1981 - L 2002 - L
1982 – M 2003-M
1983 – N 2004-N
1984 – P 2005- P
1985 - R
1986 - S
1987 - T
1988 - V
1989 - W
1990 - X
1991 – Y