The furnace fan kill switch on my unit has issues. First, the furnace filter is held down by a metal arm, the arm pushes the door on the furnace up about one-half inch killer the furnace motor. This kill switch is above and to the right of the fan motor, and when the door is in place is pushed in. When you remove door to change filter, the switch turns the fan off by moving in the direction the door used to be.

The problem is now the fan kill switch will not depress even with the door in place. The kill switch is mounted and it has some play in the box. If I bang on the door which is fully closed, then the switch will depress and the fan will run

This is a little inconvenient - every time I hear the outdoor unit running, I have to go bang on the furnace door to get the fan to run.

Suggestions?

See if you can bend the mounting tab out a bit. Although I don't recommend doing so, you can jump the 2 wires so the switch is inoperative and use the main switch on the side of the heater. For 50 or more years heaters didn't have any door switch.