1987 300E aux fan switch? Also temp gauge ?

Engine should run at about 80 degrees C. Gas engines quickly climb to

100 to 120 in heavy traffic on hot days - normal.

I'd speculate that dual numbers on switch may be low and high fan speeds. There may also be a switch on the A/C's receiver/dryer connection.

So if 105 is the fan low speed on. Does it matter weather the AC is on or not?

Also, if the AC is on is the fan always, at any temp?

"-->> T.G. Lambach

Apparently the answer to your questions vary by model and year. Others will have to give you those specific answers.

"Another question, the temp gauge on the dash has 40 80 120. There is a line slightly above the 40 is that 50? And there is a line between 80 and

120 is that 100? I noticed that the lines are not spaced evenly so the temp gauge is not linear. "

The line between 40 and 80 is 60. The one between 80 and 120 is 100. They aren't evenly spaced, which is kind of weird and leads to some confusion.

To figure out exactly how the aux fan works, you'll need model specific info, better yet, a schematic. On many cars the aux fan comes on when either the engine coolant temp goes above a certain point or the temp at the AC receiver/dryer goes above a certain point. There may also be a relay involved.

I'd take a wild guess at the switch rating and say that the 105/115 may mean that it may close starting anywhere north of 105 but will close for sure by 115.

According to ETM (for 86-89 300E gas engine), 105 turns on the aux fan at high speed (via standard cube relay), 115 turns off the AC (via Klima relay). There is a pressure switch at AC drier. It closes at 20 BARs and opens at 15 BARs. This is for the low speed aux fan (via a separate cube relay). The low speed circuit has a resistor (around 5 ohms) in series. I have seen people bypassing the resistor when it goes bad. This effectively makes the fan running at high speed when AC is on (no harm but noisier).

Are you experiencing engine overheating? If so, when (car moving or not moving)? If car moves faster than stop-and-go, the air flow is enough to cool down the radiator. If stuck in traffic, a working aux fan is really important. BTW, how is the engine fan (whose clutch is quite reliable though)?

Most of the circuits at this era is easy to test. For example, jump> Hi

Thanks to all for the replies.

I took a look at the schematic. The fan turns on high at 105C. There are two fuses and a relay that have to work for the fan to come on at 105C. Correct the 115 shuts of the ac compressor. Interesting that it takes 2 fuese as One fuse provides voltage to the relay coil and the other fuse is the voltage that the relay switches

I'm going to jumper the fan relay and see if the fan turns on , if not I'll check the fuses, then the relay and wiring and the fan itself.

Thanks for the input.

I just spent time on my E300D 1995... should be similar enough to your car.

Two trigger for the fan... low and high speed. The low speed is triggered by your accumulator/drier... with either green or red switch... these are temperature switch. If you jump the two wires together here, the low speed should come on. If not, then you got problem elsewhere.

The black switch on the top of the accumulator/drier is for compressor... making sure there is enough pressure to keep the compressor from burning out due to no refrigerant.

The other trigger is for high speed and that is located on your engine in the front... two prongs probably with blue color... If you pull this harness off, the high speed should come on. If not, then you got problem at the relay. This high speed relay is the green one in the fusebox... usually should be good as it rarely get kicked on.

The blue relay in fuse box is low speed... This relay can go bad or fuse get blown. This relay triggers the low speed when the red/green switch wires are jumped.

If the low speed does not come on... it is most likley the relay is bad... or wrong colored switch red/green... or simply bad switch. This red/green temp switch required the refrigerant to be evacuated before replacing.

My problem? I put the wrong colored one in... original is red... and I put in the green one... and lo and behold... low speed never come on.

Hello, I've been searching the net for info as my 87 300E has the sam

problem--aux. fan not working at all... I've read through the comment on this thread and they seem to make sense. Can anyone tell me how yo know which relay is for the fan? I'm not exactly sure how to jump th relay either--is this done by simply jumping the correct contacts? I so, which ones? Also, the AC switch is pretty easy, but I'm not sur which one is the 105 switch. There seems to be at least possibilities on the head. Is it the one w/ the 2-wire prong and third individual prong? (that is the one approximately near the 4-5t cylinder back)... Thanks in advance for the help.

BTW, in my situation, I did run a jumper power wire direct to the fa

this afternoon and it did run, so I know the fan motor itself works. also checked the one labeled fuse and it is ok. (did all this befor finding this post) I'm not sure where the other fuse is..

Thanks in advance for the help

-- tsh2

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Your car might be slightly different but not much different. Your car is similar to my previous 190E setup. I believe you got only one speed fan.

I would first jumper the temp sensor by your AC accumulator/drier... not the black one on the top... but the one on the side... probably green or red. Touch the two bare terminals together to see if your fan comes on... If no, then you need to check elsewhere.

As for the sensors you have on the top of the engine... the two prong is for AC and the three is for engine to trigger your Aux... My suggestion is change those out due to age unless you changed them before. To change these, engine must be cold.

The relays are in your fusebox... you need to loosen 6 screws and remove the cover of the fusebox... There will be colored relay with a fuse on it... if you have two of them... blue and green, then you actually have two speed aux.

Another tip. Get a test light and see if you have 12V making it to the wire end at the fan. Often inline connectors get corroded. So, while the fan could run if you hook a wire from the battery with 12V to it, the connector to the fan could be bad on one end and the normal

12V is not getting there.

Thanks for the info. I was able to jump the ac switch as you describe

and the fan did come on. I also jumped the 105/115 switch on the hea and it came on high speed. I'm not certain that the car has gotten ho enough to activate the 105 switch, so I'm not sure if that is bad o not. As for the AC switch, the 134A was low, and I've just charged it so with out proper coolant levels, I'm not sure the switch would hav activated either. At least I know the circuits are intact and the fa does work with activated (no relay or fuse problem...) I'll have to d some add'l work to make sure the two switches are functional though..

thanks again for the info. the labeled photos, schematics, an

comments here are really helpful

-- tsh2

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What color is that temperature switch? Is it green or red? You converted to R134a... so you need a lower temp switch to activate the aux fan. The red one is used for R134a System... if you have a green one, it would never come on... just like mine.

I installed the green one when I fixed the system and realized that the factory installed the red one... I thought it doesn't make any difference but ha! aux fan never come on.

I am still waiting for the red one to come.

The red or green switches at the ac drier are in fact high pressure switches (I note many spare parts sites term them as temperature switches which is incorrect). Usually when the presure is above 20 bar the switch closes the circiut and the low speed relay is activated. When pressure goes below 15 bar the circuit is then opened and the fan switched off.

... please don't leave some of us hanging. At what pressure does the 'red' (R134) swithc and the 'green' activate? Does the 20 bar refer to both?

- cheers, guenter

A A cheers, guenter

Hmmm, I just converted to R134a on my 1989 300E... simply changed the valves and added synthetic oil, left everything else alone. Works well, the aux fan comes on right away .... darn dealer told me I had to replace my evaporator 4 years ago because of a leak they detected through the cabin vents

... even though the a/c hadn't been used in 4 years there was still R12 residual pressure and the system on this truly 'simple' reconfiguration to R134 has now worked for 3 weeks.... I'm thinking those 'sniffers' (mass spec) the dealers use are tooooooo sensitive ... BUT, they do come in handy for making money. A 'heads-up' for anyone facing a similar dilema with an expensive evaporator repair.

cheers, guenter

I couldn't find answer to that question... however, I will try. I think the red is lower for the R134 system... which is why mine never came on...

And now I'm totally confused. It appears people are talking about two different things, without being clear. On the receiver/dryer there are typically two switches. One for pressure, which is in the compressor circuit and one for temperature, which is in the circuit for the aux fan to come on when the temp gets high.

Which one is the green/red all about? And which is supposed to be different when going to R134?

The temperature switch is the on available in green or red color. I know the red one is for R134A.

There is no temperature switch in the A/C circuit. Both switches near the receiver/dryer are pressure switches. The one with green color is on at 20 BAR and off at 15 BAR. This controls the aux fan relay. The other pressure switch is on between 2.6 and 30 BAR so compressor clutch can be engaged (via Klima relay).

The W201 ETM does not mention red color pressure switch. Note that W124 is very similar to W201.

The aux fan is separately c> >