Can I hook up two external monitors (with a HDMI interface) to a MacBook Air 2012?
I don't want to use the MacBook Air monitor when the two monitors are used.
You can hook up two external monitors by using the thunderbolt port that support daisy chaining. You connect the the first screen with your Macbook air and connect the second screen with the first screen.
According to the following KB-article the following models support up to 2 displays through one thunderbolt port.
It's not possible to connect 2 monitors simultaneously through one hdmi port.
Arstechnica also has an article about the support of multiple external monitors through one thunderbolt port. Apparently the older Macbook airs only support one external screen due to limitations in the thunderbolt host controller.