Just curious - on my 86 300E should my aux. fan run at different speeds depending on whether or not the a/c is on? It seems to run at one constant (max) speed whenever it's on, whether from the a/c or just mild overheating. Isn't the resistor supposed to make it run slower under some conditions? The resistor visually appears intact and the connections are corrosion free. Is there an easy way to accurately test it? (it's sort of buried under the ABS unit, so a little hard to reach) I've done a search and didn't really find an answer for this.

Thanks for any help.

Jumper the a/c high pressure switch at the reciever/drier... that will energize the low speed fan [ using the resistor.]
High fan [ no resistor]is only when coolant temps are above 105C and has nothing to do with low fan... the two just share the same fan motor, but completely different circuits/relays/sensor/fuses...

Thanks for the reply.

Should the speed differential be quite obvious, because I can't say I've ever noticed a difference. Is there an easy way to jumper the hi-speed fan circuit to test it as well?

I am thinking the varable speeds came on later models, and an 86' has one speed only?

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

< __________________
>>

OK .
If there is a dropping resistor , it is b/c there are two fan speeds .

The high will be jumpering the 105C coolant sw..

Thanks, I was thinking the same thing about the resistor. Can you tell me where the 105C switch is located, or what color wires it uses?

Think you mean this one on top of valve cover (partly obstructed by air cleaner)
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1FX0MB1RS1G1117TI8&year=1986&make=MB&model=300-E-002&category=G&part=Engine+Temp.+Sensor
Here is a helpfull .pdf 4.1 megs:http://home.comcast.net/~martin.carney/1986.pdf Starts talking about your concern on pp A22 Arthur's point made on pp 23.
My AC has never worked on this car so I am somewhat unfamilar with proper operation.

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

The 105/115 switch [S-25/6] is on top of engine . The wire you want to ground for high fan activation is br/gn. That will complete the circuit from K9 high speed aux. fan relay , which by-passes the dropping resistor and feed fan motor full 12v.

For low fan, you jumper br/bu and br at reciever/drier switch [ S/32 } for low fan relay K-10 preresistor circuit. This feed uses the resistor in series to drop the feed voltage to fan ,resulting in low fan mode [ a/c only]