Right, that would be MCO10UW and the owner's manual is here.
The owner's manual does say this, of course,
"To prevent overheating from taking place, the exhaust
fan is designed to automatically turn on at a low speed if
excessive temperatures occur. Should this happen, the
fan cannot be manually turned off, but it will
automatically turn off when the internal parts have
cooled. The fan may stay on for up to an hour after the
range and microwave oven controls have been turned
That;'s standard on microwaves.
But these models do have a separate internal cooling fan (which should run any time you microwave) plus the hood vent exhaust fan, which should only run when you select it, or if there is an excessive stovetop or under-hood temperature.
So if it comes on whenever you microwave, that is incorrect.
When that happens, it's usually a defective vent thermal switch (a.k.a. hood TCO).
But since it's brand new, I would certainly contact Magic Chef about this. If it's in need of repair, they will fix it free, assuming the oven wasn't physically damaged.For more help from Magic
Chef / Ewave see here or their contact page.
For Magic Chef
in Canada call 866.587.2002
happy to help you with free advice and we'd appreciate your
thoughtful rating of our answer.