Just wanted to find out if the vent should be open or closed when air conditioner is on..
If you are talking about a whole house ducted system, it is best to keep all vents open.
If you are talking about a window air conditioner, the vent is mainly intended to bring in fresh air, usually people keep them closed, unless you are just running the fan only and want to bring in cooler fresh air, like in the early mornings.
If this has helped, please rate me, or contact me back with any further questions that I can help you with.
Sincerely,
Paul Gibson
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