The General Aire 77 unifilter is an inline filter that cleans fuel before it reaches a motor. The General Aire 77 fuel filter fits on many mobile and immobile heating appliances that burn oil. Unlike many small fuel filters, the General Aire 77 has threaded nozzles: rather than attaching to the fuel pipes through clamps, the General Air 77 uses threaded pipe. Although the exact location of the General Aire 77 unifilter varies by the appliance it is fitted in, replacing the filter is a straightforward process.
Locate the fuel pressure gauge on your heating appliance. Release the fuel pressure by turning the nut on the pressure gauge counterclockwise with your wrench. Clean up any fuel that may dribble out of the loosened nut.
Clamp the nut that's routed to the motor on the outlet female end of the filter with a crescent wrench. Clean up any fuel that dribbles out of the pipe and the filter onto your hands or the other components of the heater. Loosen the nut from the fuel pipe with the other crescent wrench. Pull the loosened fuel pipe out of the fuel filter. Clean up any spilled fuel.
Repeat Step 2 for the inlet female end -- the end receiving fuel from the fuel pump -- of the General Aire 77 unifilter. Pull the General Aire 77 unifilter out of the inlet pipe and set it aside.
Thread the outlet pipe into the female end of the replacement unifilter and tighten the two together with your wrenches. Repeat this process for the inlet side of the fuel filtering system.
Tighten back on the pressure gauge nut that you loosened earlier. Add fuel to the heating appliance if the fuel level gauge is low from having lost fuel in the replacement process.
