The GeneralAire 12740 is the correct replacement for the following air cleaner:
The GeneralAire 12740 Air Cleaner Cabinet Assembly is a complete cabinet assembly for the GeneralAire AC-1 Air Cleaner Model. The air cleaner cabinet is installed in the return air system. After the media frame is inserted into the air cleaner cabinet, you want to make sure that the airflow arrow on the media frame is in the same direction as the arrow in the cabinet. The plastic pleat spacers are always on the downstream side of the filter media. Replace the cover and thumb screws.
GeneralAire 12740 Air Cleaner Cabinet Assembly specifications:
If a condition indicator is used, be sure that you install on it on a vertical duct surface between the air cleaner and the furnace blower. GeneralAire is also known by the following spelling variations: GeneralAir, General Aire and General Air.