The floor vent is only snapped in place with 2 tabs in the front and 1 in the back.
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The white duct is secured by 1 screw. wiggle it down the pull to the passenger side to remove.
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Here is what is left. The heater core housing is only held by 1 nut on the bottom right. and 1 screw on the left above the gas pedal.
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I rolled it down and out like the AC evaporator housing.
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Here is the heater core housing removed. To split the case there are a few screws and several metal clips. Make sure the metal clips don't go flying across the room.
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