I need a parts manual to find the pre-ignition blower that cleans out the system prior to the unti igniting the gas. The service tech couldn't find one anywhere.

Seems that unit was made around 1990 so parts should still be available.

Call here for parts

Carrier Temperature Actuated Switch P/N HH18HA449 [HH18HA449] - $32.00 : Shortys HVAC Supplies, Short on Price, Long on Quality! - Indianapolis, IN