I have a 1997 Ford Expedition with a seemingly random Hot/Cold air swapping issue. In the winter, when I turned on the heat, it would randomly alternate between blowing freezing cold air from outside, and blowing burning hot air from the engine. Now that summer is here, a similar problem seems to persist with the A/C. Sometimes, it will blow nice cold air from the A/C, and sometimes it will blow burning hot air that's much hotter than the outside temperature even on hot days.
I can't seem to recognize any pattern to the switching. The problem was just in the front vents, with the rear vents always working fine, until just a couple days ago, when the rear vents also started doing the same thing.
I'm assuming that since I still sometimes get freezing cold air, that I'm good on Freon. Also, since I get burning hot air, and never just warm air, I'm assuming that the A/C isn't just intermittently failing. My best guess is that the car is blowing hot air straight from the engine, but I'm not sure what's responsible for that. Does anyone have any experience with this particular issue, or even just the heating/cooling system in general? Any tips at all would be much appreciated!