Why are there two air filter slots in my HVAC system?

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Using one hand on each side remove the used filter from the filter slot and replace it with a new Filtrete™ air filter filter cover toward the air purifier

airbet88 slot online Save energy, money & keep air fresher with a filter seal Its unique design & magnetic strip keep it in place & allows it to fit into most filter slots

air filter slot cover essentially you want air being sucked from the return air vents through that filter, NOT bypassing around it If you can't buy, or get a cover