Brian,
I believe this was manufactured January or March of 1990, based on the serial#. Carrier, Bryant, Payne all used the same system. The first four didgets were the week and year. Since you only have three didgets, I'm going with the third week of Jan, 1990.
But HVAC guys get up early. Call one of them in the morning to verify. And the parts houses are open even earlier.
