1987 300TD - Fans

[zu!]

I've been searching around the forum trying out all kinds of leads to figure out if my fans are not working right. Here's what I got:

1. Main viscous coupling. It's a 9-blade plastic one that doesn't start with a roar and at operating temps (80-82) spins really slowly to my eyes. When engine is shut off using the engine stop lever, the fan continues spinning for at least 7 revs. Is my fan shot? If so, I've read about using the fan from a 603. Is this the right part to change it with?

2. Aux fan. I have just one. My understanding is that it should come on the moment aircon is switched on. It doesn't. I pulled the wires off the blue sensor on top thermostat housing. It's a 3-prong thing, but one prong has its own wire. Shorting the two wires makes the fan turn, but not fast.

From what I've researched, shorting this should make the fan go on high speed. My research then says to look for the fuse on top of the "green relay". All my relays are silver. Here's a pic.

Which relay should I check and how do I check it?

There's also some reference to another sensor with a wire 6" pigtail. I read that I should peel back the insulation and short the wires to test the low fan circuit. I can't seem to locate this wire which is supposed to be above the drier. Heck, I can't even find the drier!! I know that's the thing with the window to look for bubbles right?

And finally I read that I need to check the porcelain fuse. This lies under the abs unit. It LOOKS intact. But does one get ones hands in there to unscrew and check it?

It's probably all very easy. But boy oh boy, uv been searching and searching and end up getting more confused! Help!


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[Mxfrank]

First, the main fan is controlled by a thermostatic clutch. It comes on at around 95C for most Benz's. The aux fan will come on in only two situations:

1) It comes on at low speed when A/C pressure reaches a threshold, I believe it's 300psi, well above normal pressure. Reports of it coming on every time the a/c is turned on probably mean the a/c system is ovrercharged.

2) It comes on at high speed when the car is close to overheating, probably around 105C.

So if you want to see the fans coming on, you'll have to work for it.

The a/c dryer is located behind the left headlight on most Benz's. There are two switches that should be screwed into it: the switch on top of the fitting will be the high/low pressure switch, nothing to do with the fan. The one on the side of the fitting is the fan low speed switch. If you short out the leads, the fan should come on. Do not remove or attempt to replace this switch, as it will empty your freon. Have it done by an a/c shop.

[treetops]

Zu! to Q1)IMO yours is headed towards not functioning if not there already. I've replaced the main fans on both my cars and they are fairly constantly on in this current weather. The def Roar when I 1st start then either continue or disengage as needed, but the Roar is def audible, cant miss it. Also, both stop dead in less than 1-2 revolutions on engine stop.

[jay_bob]

Use the 606 fan and clutch

606-200-01-22 clutch
606-200-01-23 fan

See this post for the fan sequence of operations
W124 A/C - new pressure switch, auxillary fan worked twice, now nothing...

[zu!]

Thanks Jaybob! I'll be looking for the 606 one then.

Also it appears that when I shorted the leads at the top of the engine that must've been the high speed.

I guess I'll be changing my fan soon! Thanks for the help all!


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