AUxiliary electric blower fan - where's the relay?

[s class]

The electric blower fan in front of th radiator has quit on my 280SE. Yesterday I got to investigating, and found that the fan works when given a direct supply from the battery. The cabling all appears in tact. The 100 degree switch is good too. I established that it must be relay controlled, and probably the relay has given in. But where is the blasted thing?

In my engine bay fues box I have only one relay - for the fuel pump. Under the driver's side knee roll, there's a row of three. The rear most one is for the aircon, the front most one for the electric windows. The middle on, well I can't ascertain what its for, but replacing it didin't help the fan.

Higher up under the dash are the flasher relay, and another large one in a black plastic box. What's that for?

Any help appreciated. Thanks.

 

[BAR]

You can find manuals for this on the W116.org site in the Library section.

The fan is triggered by two events and has two separate inputs to the relay:
1. Engine water temp >100 deg C
2. Air con coolant > 62 deg C

Temps may vary from model to model, but this indicates that you should also check the two thermostats.

You can also set the fan to 'permanent' on by 'jumpering' the circuit at the A/C receiver/dryer [located next to the aux fan at the front of the condensor / radiator]. disconnect the two electrical plugs [bayonet fittings] and join them together. This will ensure the fan operates whenever the ignition is switched on.

By the way, on my 450 I have not yet hit those temp ranges becasue the viscous clutch fan does a more than adequate job.

 

[s class]

Thanks BAR, I will put that info to use in th nxt couple of days. My 280 has always had marginal cooling performance, and its worse at the moment because th viscous clutch is way short of its best. I think I may need to spring for a new one - but in any case I'd like th aux fan to be working.

Incidentally, the high refrigerant temp trigger for the fan has never worked on this car. I guess that thermostat may be suspect. Can it be tsted / replaced without loosing the refrigerant?

 

[BAR]

Can the condenser thermostat be tested 'in-situ'? I don't know the answer to that question, but would be curious myself to know the answer.

I have recently had my refrigerant refilled, but still get marginal cooling. It seems to work best when the vehicle is stationary. I have tried running the aux fan permanently 'on' without any benefit. So with the limited amount of free time on my hands, I am still attempting to find out answers myself.

As for the viscous engine fan: try sending a PM to Styria. He was able to supply one to me. Replacing it is relatively simple, and can be done in less than 1 hr.

1. Loosen up the bolts that hold the fan to the engine. If the fan rotates, apply some pressure to the fan belt to grip the fan.
2. Loosen the power steering pump to allow for slack on the fan belt.
3. Undo three of the fan bolts and rotate it slightly, then replace two or more of the bolts with the fan out of the way [this ensure all stays in place and the fan belt and mounting positions are held.
4. Undo the two bolts on either side of the fan cowling [at either side of the radiator], this will need to come off together with the fan as there just isn't enough clearance for the fan to caome out by itself.
5. Remove the remaining fan bolt.
6. Take the fan and cowling out of the engine bay.
7. Undo the bolts that hold the fan to the clutch.
8. Bolt the fan to the new clutch.

do the steps 6 through 1 to refit the assembly.

Caution, when moving the power steering pump, ensure that you do not loosen the fluid line bolts, or else ensure that they are securely fastened before driving again [it's amazing how quickly the fluid will be forced out even if only 10-15 degrees of rotation on these coupling bolts].

 

[Bandolero]

"Incidentally, the high refrigerant temp trigger for the fan has never worked on this car. I guess that thermostat may be suspect. Can it be tsted / replaced without loosing the refrigerant?"

Yes you can. It just unscrews from the Receiver/dryer.
Make sure you do the correct one as the other one is for the safety shut-off for low refrigerant pressure and you will "dump" all your refrigerant.

 

[s class]

BAR, when I said marginal cooling - I meant that my car's radiator gives marginal engine cooling performance. My A/C actually works very well - we still get R12 here
My car's a 280 - the fan is driven off the alternator belt, not the steering belts like the v8's. Its actually pretty trivial to remove the fan clutch. I must just get around to pricing it on Autohaus aswell. I'm placing a big order there soon, so hopefully it will only be a marginal increase in postage.

Bandolero, thanks for the caution about unscrewing the correct sender from the drier. If I'm unsure (I'll look at the car tonight) I'll post up a photo before I unscrew anything.

 

[s class]

Clutch is US$186 at Autohaus. I suspect it will be tough to beat that.

 

[BAR]

"Incidentally, the high refrigerant temp trigger for the fan has never worked on this car. I guess that thermostat may be suspect. Can it be tsted / replaced without loosing the refrigerant?"

Yes you can and without removing anything from the car.

Simply put the ignition 'on' without running the motor. For the refrigerant temp - turn on a heat gun or hair dryer and driect the air towards the thermostat: once it gets hot the fan should switch on. For the enigine coolant, which would be the quickest way to check your relay, unplug the single electrical lead from the thermostat housing above the water pump, its a round bayonet fitting, and push in a piece of wire, then ground that to the engine block: the fan should switch on as this lead 'switches to earth'.

If it doesn't switch on then look at the relay.

 

[Bandolero]

Don't forget to turn the A/C on as well.
From what I've noticed these cars are set up so that the electric fan only comes on with the A/C on and when the temperatures rise too high.
I rewired mine so that the fan will come on even if the A/C is not on.
(Of course only if the temp gets to 100c.)

 

[BAR]

Not necessary to turn on the A/c: just make sure that ignition is on. Don't need to have engine running.

This test is a functional test for the Fan and Relay only.

i.e. If either the A/C or Coolant 'switch' is in on position [as would be when trigger temperature is reached] then the fan should turn on. You have already identified that your fan works, so you are now checking that the realy is OK.

 

[s class]

I;ve checked out these issues - the fan runs when given supply directly from the battery. WHen I ground the temp sensor lead at the cyl head, nothing happens. So its either the relay or wiring associated with the relay.