Does an A/C unit need a closed door or a vented one? or none at all?

[Luney]

We Have two central a/c units in our 5 bedroom house. The upstairs one is in the Laundry room and has no vent on the door. we Noticed it pulls the door shut when it goes on. I figure this means the a/c unit needs to intake air, so I prop the door open and have been asking my mother to get a door with a vent so that I can Install it. She has vehemently refused and closes the door whenever she finds it open. she swears it Costs more money leaving it open, and makes the a/c work harder. who's right? by the way, the downstairs one has a vent in the door but you can still feel the pull if you open it while it is running.
I forgot to mention the a/c unit is in it's own room in the Laundry room. It's that Door that I am referring too. NOt the Laundry Room Door, although this pulls hard as well when the A/c is running and I have propped the A/c door open.

 

[ragtops]

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In a central a/c system, air moves under pressure from the a/c fan cabinet through the supply ductwork into the rooms and then from the rooms through the return air ducts back to the fan.

Air being sucked into the a/c room through the doorway can happen if:
1. the nearest return air opening is in the a/c room
2. the return air side of the ductwork in the a/c room has an air leak - and it would have to be a big one to pull enough air to hold a door closed
3. your return air ducts are partially blocked, preventing normal circulation - dirt-filled filters in the ducts or in the a/c cabinet are the main cause

Check your ductwork for blockage and/or for air leaks. You do not need vented doors.
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