Mac mini losing signal over vga when using adapter.

At my church we are installing 2014 Mac minis in the classrooms and occasionally when we power them up the main display works perfect but the projector which is plugged in through the mini display port to vga adapter the screen will just be blue like it does't have a signal. When I check in system preferences the computer shows both displays plugged in though. Powering off the projector doesn't fix the problem I have to manually unplug and replug in the adapter.