2001 330xi: Climate control fans surges and wanes

My climate control fans surges and then drops off on my 2001 330xi. It seems to happen when I'm either using auto control or when I'm using the manual controls. The current temperature here in Philadelphia is
around 50-70 degrees Fahrenheit. I'm seeing the problem with the heater/cooling fan surge at all temp settings....it seems to come and go. Any thoughts. Could it be a filter? I'm perplexed because it comes and goes, but seems to happen most of the time when I'm driving (especailly when I slow down, for example). Thanks!
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Almost certainly the final stage resistor.
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*Caution: I drive like you do.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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"Dave Plowman (News)" wrote:

I agree with Dave. Although now instead of a resistor pack it is a transistorized control unit. Just had the one in my 97 328 fail recently.
Frank
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Interesting. It's know as 'the hedgehog' by the trade in the uk due to the rods sticking out the back which I assumed were resistors placed in the air steam for cooling. I've not got a wiring diagram for my car.
They appear to have improved. They seemed to last just over a year when I first got the car, but this present one (the only one I had to pay for) has done three so far. They must have cost the maker a fortune in warranty replacements.
I kept my old one intending to open it up to see what is inside but ran out of tuits. ;-)
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*Am I ambivalent? Well, yes and no.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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"Dave Plowman (News)" wrote:

Hedgehog - that's right. I couldn't think of the word when I was writing my reply. I used to think the presence of the microfilter tended to reduce the airflow through the vents, compared to my other car, but when I pulled that hedgehog sucker out it was apparent that those cooling fins are at least as much to blame.
Frank
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Ah, I see this one now...transistorized control unit. Thank you very much. Off to the shop then, I suppose.
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Thank you....sorry, didn't check back for a few days (was on a business trip). Will get that checked out, then. Final stage resistor. Hmm.
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