1993 Ford Aerostar heating and cooling

They are probably corroded due to anti freeze try a propane torch if you can get it that small and heat housing then tap with a small hammer where screws are then try to loosen bolts, but don't be surprised if they break.

Then it's drill and tap time or a rethreaded if the threads are damaged to much. Or if it's screwed up all together then whatever it bolts to. If you can find or have one of those little butane torches may be better as they are smaller and easier to fit in tight places. Remember heat with torch, cool with oil an d tap with a small hammer do that a like 5 ties each bolt