The maintainance cover also emits an signal on the opposite side that can be used by an transmitter there. For activity it is needed to check the input hatch.
So, Blood, I remember I tried putting the machine controller on the bottom side of the Vacuum Freezer (just to test it), and then put the controller on the multiblock. Then I put a lever on the frostproof block under it, but it won't activate. Shouldn't work?
Why can't we use the sides of the controllers, like this: