You said door so I am guessing it has barn doors?
If so when you open them you will see a row of pins that look like copper. They corrode so they may look green in color. That is what sends the power to the door itself. When the door closes they come in contact with the door part of connection to the grid.
They get green and dirty, they don’t send power to the window grid. If they are dirty or green I have used fine emery paper to clean them.
But you also need to look at the grid on the windows themselves for any damage to the grid on the window. Over the years the windows get washed many times and if you are not careful you can damage that grid causing some of the grid lines not to work. They heat up and actually do the defrosting.
If the grids are not working in just a few places look for brakes. You can get a repair kit, basically a eclectically conductive paint. Use tape to make a nice clean line, brush on the paint in the places that the lines are broken. Let dry and recheck to see if they work again.