mircowave with crack on door window

The microwaves go through glass which is why you can use glass containers in the oven.

Is the mesh part of your microwave door intact?

The metal mesh is what keeps the microwaves inside the unit. If the glass is cracked you lose some protection for the mesh.

Damage to the mesh may now be greater.
Maybe it's time to replace the microwave.

If the mesh in the door is still intact, it is probably fine to use it.  However, you might be better off just replacing it.  When mine dies, I plan to install a simple hood with light over the oven and just buy a counter top microwave.  They are way cheaper and easier to replace, and I just do not like having electronics right over steaming pots.

let me clarify to nickg5 and Michael Byer, i am actually NOT using the microwave part, just the lights and fan that come with it.

Thanx