My 1991 420SEL (W126) is making a high-pitched squealing noise from the area behind the passenger-side dash. It sounds like a bad bearing on a fan of some sort.

What puzzled me is that the noise is independent of the main ACC system blower fan, and is unchanging regardless of blower fan speed, and further the noise is still present even when the ACC system is turned completely off.

I took things partly apart, including removing of the lower cover that is underneath the main blower (but without removing the actual blower motor/fan).

In poking around a bit, I found that the noise is coming from a small little fan (maybe 1-2" in diameter) that is tucked up next to the main blower fan. (It's on the side that is towards the passenger door). I can actually make the noise go away temporarily by pushing on this fan a bit, or by stopping the fan with my finger-tip.

My questions are:

- what is the purpose of this fan? It is basically on/running at all times, as far as I can tell.

- It's not clear what other pieces I'd have to remove in order to replace this fan (once I figure out what part it actually is.....), so if anyone has any tips or suggestions, I'd love to hear them!

- I also wonder what harm would be done by just disabling the fan in some way. Obviously this depends on figuring out what its function is. (On the theory that it will be easier and cheaper to just make it stop, than it will be to repair/replace it....)

This car has got 210k miles on it, and isn't worth too much at this point, so I'm not crazy about spending too much on this issue. But my wife still likes driving the car on occasion (it's sort of our "spare car" at this point), and the noise is way too annoying to live with!

Thanks for any ideas that anyone has.