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Random interior fan activation?

Started by Howard60, 25 April 2020, 06:23 AM

Howard60

This is a weird one. Took my 280se out to deliver necessary items to mother-in-law.
After being out for an hour or so, the interior fan suddenly came on, and continued on full blast
for the trip home? None of the dials or sliders made any difference, and when I stopped and restarted the engine
it carried on!
I left the car to cool (it was a hot day, the first the car had encountered since Ive had it), restarted it to put it back
in the garage and the fan didn't come on??

Has anyone experienced this?
Its nice to have automatic 'climate control' but not if i dont want it, and it is very loud!
Strange?
Howard
Previously: 280ce W123, 450slc C107, 350se W116, 230e W123, 250ce W114

mrkozzy

Sounds like "mother-in-law" issues to me.

But seriously, have you had anything re-wired in the car recently or in the past?
I've just found out my airconditioning man rewired the system so the front electric fan is "always on" which is incorrect.

I've been bewildered why the front of the car has been noisier than normal.

Just a thought
MrKozzy

Howard60

Hmmm? I did remove the Becker radio to clean it?
Maybe I disturbed something then?

Strange that it randomly happened 30 miles and several hours into the driving day?

Ill see what happens if I can take it out again for legitimate reasons, or after lock-down?

I might check the wiring behind the radio too

Cheers
Previously: 280ce W123, 450slc C107, 350se W116, 230e W123, 250ce W114

Howard60

Now fixed, removed the switch from under the wipers, and bent the filament back so it didn't make contact.
Now it works perfectly. No idea why it had this, I dont have aircon?
Previously: 280ce W123, 450slc C107, 350se W116, 230e W123, 250ce W114

daantjie

That is the blower resistor thus not dependent on you having ac or not.
Daniel
1977 450 SEL 6.9 - Astralsilber

hamidagha

Interesting! Mine has been doing the same recently so I just took the fuse out. So when you say you bent the filament back do you mean it was warped with age? I will look at mine tomorrow.

hamidagha

Quote from: Howard60 on 01 June 2020, 03:57 AM
Now fixed, removed the switch from under the wipers, and bent the filament back so it didn't make contact.
Now it works perfectly. No idea why it had this, I dont have aircon?

Great hint Howard60. I just did this and fixed my issue too. While I was at it, I straightened the wipers too which have been bugging me for a while :)

ptashek

Classic blower motor resistor issue. There's a bimetallic strip there acting as a temperature fuse of sorts. The way it works is that if the resistor gets to hot, the circuit is shorted to ground thus making the fan go on full blast without any control, until the resistor cools down again.

With age, that "fuse" rusts and shorts randomly and sometimes permanently. The simplest course of action is to simply bypass it. Another option is to have it fixed, or replaced with a new unit which is still available from MB the last time I've checked.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE