Auxilary fan issue on 92 500SL

Hello, I have a 92 500SL that I recently bought, and I noticed that only one of the auxilary fans works. I was wondering if this is normal. I have searched this forum for quite a while trying to find out whether or not both fans are supposed to start up together, or separately. I know that the dead one (the one on the left, when looking at the front of the car) is altogether, not running, because even after 80 degree runnig conditions, it still doesn't run. So all I really need to know is if those two fans in the very front of the car start up together, or separeately, and what the best way to go about fixing this problem would be if they start together. Thank you.

[Gilly]

Thay both are supposed to run at the same time. I'd assume it needs a new fan motor, you should be able to buy just one of them.

Gilly

[LeaUK]

Mine run together and switch on at around 110C, although I'm not sure what temp they should switch at. Gilly, have you any idea?

Cheers
Lea

[Gilly]

110 seems a bit high, may be correct though. The gauge could be off a bit too I suppose, I'd assume closer to 100C, but I could be wrong. You should see them come on at low speed fan position with the AC on based on AC system pressure. With the engine temp switching on the fans it would be high speed fan position. But to clarify, the fans should BOTH run, it's not like they are individually controlled. Just like turning on your headlights, there's not a switch for each one.

Gilly

[bobterry99]

You can remove the fan assembly fairly easily. With a 10mm socket you unbolt the "X" piece in front of the fans and the crossmember which it attaches to above the fans. Then you remove three bolts which bolt the assembly in place and withdraw. I performed this operation just a few days ago on a 300SL.

[LeaUK]

Uhm, interesting. You say there are two fan speeds. I've only ever seen one on mine and that seems to occur at 110C coolant temp. BTW - I have ordered all three new coolant temp. sensors

Should I see fan speed one immediately after I press the EC switch then? Most euro cars switch the fan(s) on immediately and therefore I would expect the 129 to also.

[Gilly]

The low speed fan is controlled by AC system pressure. With the EC button, this cuts out the AC compressor, so I am willing to say that the fans won't run on low speed with the EC button pushed.

Gilly

[LeaUK]

Sorry Gilly, poor explanation - I meant with the A/C engaged; the EC switch non-illuminated.

Should I see low fan rpm immediately after engaging the A/C or at some system pressure increase? Does the system pressure increase immediately after the A/C is switched on (therefore the fans turn on subsequently) or does the pressure rise at some later point (maybe temperature increase or something else) and the fans are switched on accordingly?

Cheers

Thank you very much for all of the answers, sorry I didn't have a chance to reply earlier, but I ordered a new fan assembly, should be here tomorow. Thanks again guys!

[JimF]

temperature or pressure. Check my MENU #18 for the temp and pressure that should engage the fans (click the 'www' icon below).

Briefly, with the A/C OFF, the fans should come on around 100C, on low speed.

Mid or High: Run the car on the highway on a 90F day and shut off the engine for 3 - 5 minutes. Then start it up; you should hear the fans roar since they will come on at MID, maybe HIGH speed for a few minutes.

With the A/C ON, the fans should come on around 14 to 15bar independent of temperture.

That's it in a nutshell! Look at the table (in blue) for all the various combos.

[LeaUK]

Hi Jim

I have indeed reviewed your web page but I'm unsure if my 119.972 has three speed settings.

Not being an A/C man, I don't understand what/how the A/C system pressure is related to anything. I have been told that this pressure is usually constant and most cars just switch the aux fans on immediately after A/C is switch on, so I ask myself why MB monitors it? Does the pressure increase with A/C rad water temp? Why does the car monitor both pressure and coolant temp (via the aux fan sensor) - this is only fitted to vehicles with A/C?