Electric fan in 300sd - Page 2 - PeachParts Mercedes-Benz Forum

braverichard · #16 10-17-2005, 07:28 PM

There should be two sensors on the rec./drier...one is a pressure switch, which has a "female" threaded connector that screws onto a male threaded port...this obviously connects to the interior of the system...i.e. if you removed this sensor when the system was charged, all the refrigerant would drain out. This pressure switch connects to the compressor circuit.

The other sensor has a plastic collar around it, and it has a brass male screw connector that screws into a female threaded block that is NOT continuous with the interior of the system...i.e. if you removed this from a charged system, no refrigerant would leak out...this is the temperature sensor and is connected to the aux. fan circuit.

In the picture attached, looking at the receiver-drier from the top down as it is installed in your car, the temperature switch is connected to the top connector and then the pressure switch goes on the lower connector.

I actually don't know where the coolant temperature switch that controls the aux. fan is located. However, my thinking is that it is the same as the switch located right next to the thermostat housing which sends the signals on the temperature of your coolant to your gauge.

You did ensure that you have the correct fuse in place for the aux. fan and that's the fuse is in good shape before you started all this right?

Bruce Bonds · #17 10-17-2005, 07:45 PM

1985 SD. Braverichard, thanks for your input concerning the refrigerant temp. switch. I did a search and got a lot of info. from a previous exchange between you and MarkM. I'll troubleshoot this switch and check back. I think you are right about the location of the coolant temp. switch. I have two sensors in the area of the t. stat.

jbaj007 · #18 10-17-2005, 11:00 PM

It looks like this:

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1N017QN8K1N11D8Z4K&year=1985&make=MB&model=300-SD-002&category=All&part=Auxiliary+Fan+Switch

Bruce Bonds · #19 10-17-2005, 11:57 PM

1985 SD. I disconnected the two wires from the refrigerant temp. switch on the dryer. I turned the switch-key to the "on" position with the a/c "on". I connected the wires, bypassing the switch, and I could hear and feel the relay working. Is the fan supposed to spin when you do this test? I believe it is. I switched a couple of the silver cube relays around and still nothing. Like I said before, the fan spins fine when 12 volts are applied. What can I try next?

jbaj007 · #20 10-18-2005, 12:25 AM

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1N017QN8K1N200UJBM&year=1985&make=MB&model=300-SD-002&category=G&part=Aux.+Fan+Resistor

Find this on the firewall and test it (may be cracked). It's a resistor that is in series with the aux fan.

pawoSD · #21 10-18-2005, 12:39 AM

Mine seems to be sensitive, I have non functioning A/C, but it always comes on if I leave the car idling for a while (temp gauge showed 87C today idling for 10 mins and it was running the electric fan) I think its just trigger happy to use it.

During the hotter months I can hear it come on while driving sometimes even, (even if temp is completely normal).

Bruce Bonds · #22 10-19-2005, 06:47 PM

1985 SD. Jbaj007, I was afraid someone would suggest checking that resistor. Mine is under the brake M.C. and all of those ABS metal lines. I can barely see it and I guess I will have to take a lot of brake parts off to get to it. Oh well, more fun coming up.

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