How to free up fresh air vent door?
I think if you have already been soaking it in WD40, things are not likely to get much better with other products. But if you do pursue this rout, you just have to gauge the amount of force applied, and not exceed more than can be handled by other areas to avoid damage.
Real risk is as you are working it up and back to loosen it up, the stress is transferred to the housing attachment rivets. What is likely to happen is the hinge and cover will rip the rivets out of the body and you will end up with damage there. Alternatively the hinge will bend at either end before actually freeing up at the pivot points where it is rusted stuck.
What I would opt for if it looks like things are not going to get freed-up without risking damage, is to carefully use a file or die grinder to remove the two rivets holding the door and hinge together. You file the head off and the rest of the rivet will drop out. You can then just clean-up the hinge pivot point surfaces and either use pop-rivets or screws with self locking nuts to snug things up without binding.
You can also remove hinge and cover by carefully using a file or die grinder to remove the two rivets holding the door and hinge to the main body, and reinstall with pop-rivets or screws. This would allow you to do as cudascott said, and drop it into evaporust, and be able to work on the door/hinge assembly on a workbench with tools, vise, etc., directly putting more force into the hinge pivot points to free them up.
I think if you have already been soaking it in WD40, things are not likely to get much better with other products. But if you do pursue this rout, you just have to gauge the amount of force applied, and not exceed more than can be handled by other areas to avoid damage.
Real risk is as you are working it up and back to loosen it up, the stress is transferred to the housing attachment rivets. What is likely to happen is the hinge and cover will rip the rivets out of the body and you will end up with damage there. Alternatively the hinge will bend at either end before actually freeing up at the pivot points where it is rusted stuck.
What I would opt for if it looks like things are not going to get freed-up without risking damage, is to carefully use a file or die grinder to remove the two rivets holding the door and hinge together. You file the head off and the rest of the rivet will drop out. You can then just clean-up the hinge pivot point surfaces and either use pop-rivets or screws with self locking nuts to snug things up without binding.
You can also remove hinge and cover by carefully using a file or die grinder to remove the two rivets holding the door and hinge to the main body, and reinstall with pop-rivets or screws. This would allow you to do as cudascott said, and drop it into evaporust, and be able to work on the door/hinge assembly on a workbench with tools, vise, etc., directly putting more force into the hinge pivot points to free them up.