I think I have the switch and fan problem sorted out - so I at least know how to test the switch once I get a working fan.

I don't know about the recirculating flaps either - I do know that this system, at best, uses 80% recirculated air and 20% fresh air, which has to effect efficiency and cooling performance. But, I don't know for sure about the flaps??? Symptoms or how would I check?

ryan

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

OK, I got a new aux fan installed today and now it runs all the time - whenever the car is running. Any ideas as to why?

ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

First, see if you have continuity through the temp switch. Then advise.

Are you talking about the temp switch on the drier, or on the thermostat housing? Both switches, according to the FM, activate the auxiliary fan.

ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

I was thinking about the switch on the drier. On the later models, that is the only switch for the aux fan. You should not have continuity through either switch if the engine is cold. So either a switch is stuck closed or the relay energized by the switch is stuck. Or somebody rearranged the wiring.
The fact that the fan runs all the time might expain why your old one had failed. Which is not to say that they don't fail otherwise.

According to my readings and if I'm doing it right, both switches are showing continuity when engine is cold??

They are both reading about .6 ohms.

ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

Auxiliary fan comes on when I turn on the ignition - checked the 2 switches with ignition on by pulling the leads off. Fan did not stop running when I pulled the thermostat housing switch, but it did shut off when I pulled the leads off of the AC drier - and I could hear the relay click at the same time. So, I am assuming the temp switch in the drier is bad. Right?

ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

Sounds right to me. If you still have the original style drier, the switch can be replaced easily. If you have have certain aftermarket types, you will have to evacuate the a/c system first.

If your switch looks like this, you have the old type:
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1PY1E2LZD1SA0ZFBDR&year=1978&make=MB&model=300-D-002&category=R&part=A%2FC+Temp.+Switch

My fan will not run even the temp switch leads are shorted together.
Where is the relay located that controls the fan truning on and off?
1979 300SD

Using a jumper to provide 12 volts does turn the fan on.

If you are not sure, loosen up the temp switch real slowly. The original type has a M6 x 1 thread and the whole base is copper colored (once you clean it). I tested mine recently and it does indeed open and close pretty close to 52C.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.