Client called to have furnace serviced. Tech went out furnace manufacturing date says it from 1987. Carrier crusader furnace. Ducts are dirty and furnace filter should be changed out. Tech tested the heating system: checked gas pressure, temperature, exhaust fan amperage test, blower motor amperage test, flame rectification sensor test, exhaust fan vacuum test, ignition system tests, pull and inspected blower motor assembly and their capacitors. Inspected both heat exchangers for any deficiencies. Tevh found the igniter and flame sensor are wearing out as well as the burner assembly is getting dirty and should be clean. Tevh informed client that the system is operational at this time however the furnace igniter and flame sensor should be replaced. Client thanked us for coming out.