Fan not coming on
 

I have an E220 coupe, and today I noticed that the fan would not come on.

There is only 1 fan in front of the radiator/air con condenser, and one which is behind the radiator, and is ran off of the engine. The one off of the engine was on, but the one in front of the radiator did not come on at all.
I had A/C blasting, outside temp was 28 degrees C, engine temp would go up over the 80 mark and peaked a bit lower than the next line above 80.
I opened the hood and flicked the fan to start but it didn't.

What would I do to diagnose the issue?
When should the fan be going on?

Any help is greatly appreciated

Responded in your coolant post but,

Your engine is supposed to run just over the 80C hash mark. The auxiliary fan (in front of radiator) will only kick on when your engine temperature goes slightly over the 100C hash mark (~105). The fan attached to the engine runs all the time (obviously)

Not sure about YOUR car because it is not a US model. With MOST cars employing an electric fan in front and an engine driven fan behind, the electric is activated upon excessive high side a/c pressure to bring the pressure down.

Well, the engine may not have reached 100 degrees, however the A/C was on (and I put it on the highest setting to test it) and the fan would not kick in.

Is it possible there was just no need for it to turn on?
I read somewhere I can "trick" it into coming on? Or even modify it to come on earlier than 100 degrees?

Thanks for the replies guys, the car holds grave sentimental value to me and it is very important it runs 100% all the time.

Yes the engine temp sensor on the intake and the reciever dryer sensor can both be "jumpered" to kick that fan on. Also check strip fuse on the driver side strut mount in the tootsie roll sized case.

Can you please give me some more detail?

Ok, so from searching I have gathered that if the A/C gas pressure is low, the fan will not come on.
Is there a way to test the pressure? Or should I get a mechanic to test it, and if so, what should the pressure be?
I got the A/C regassed less than a year ago though, as the fan played up and some switches were changed.

The other possibilities are faulty switches, or a faulty fan.
Is this correct?

Can anyone tell me the easiest thing to diagnose and how to do it?
Thanks

Freon pressure can be tested with a freon charge bottle with gage from an auto store for about 22 dollars.

You can jumper the switch on the dryer and fan should come on if it doesnt check the strip fuse on the firewall. If there is voltage getting to the fan its the fan motor.

What year is this car???

Gilly

Late 1994

Guys,
Are these the wires I need to "splice" to see if the fan isn't working due to low pressure?
http://i26.photobucket.com/albums/c1...83/MercFan.jpg

I took the plugs from the wires in the red circle, and with another wire made them touch each other but the fan did not go on with the car in the ON position.
Where would the fuse be for the fan system?

yes, but don't 'splice' them/cut them....just expose the metal connector under both white plugs, and while the car is running, hold a wire and let it touch both connectors. they should come on....

I didn't cut them, I just didn't know the proper word to use. Jumped them???

Anyway, they don't turn the fan on, but the brown wires to the left do which I came to the conclusion that these are the wires I was looking for

My bad :)

I was also talking about the brown wires......yes, those are the ones to jump...

Well with those wires jumped, the fan does turn on
So now I guess I will take the car for a gas refill, even though it was done less than a year ago.
I am hoping that they simply didn't fill it up completely last time

As I said originally it is excessive HIGH SIDE PRESSURE that turns on the electric fan on most models. The green connector in your picture should be the high side pressure or temp sensor. Whether it is actually measuring pressure or temperature doesn't matter. Temp can indicate pressure and vice versa. It is possible that you would NEVER hear the fan come on even if it is working properly. The fans purpose is to bring down EXCESSIVE high side pressure. If it never gets excessive, the fan will never come on.

If I were you I would jumper just long enough to make sure that the fan is operational and then put it back together like it's supposed to be. Let it work as designed. Those guys in Stuttgart have things pretty well figured out.

Spetz, you're picturing the wrong sensor. The one you circled is for the A/C compressor, not for the aux fans. As Larry said, the green sensor is the high pressure switch that controls aux fan operation, and it just gets jumpered, not spliced. In other words, find anything metal, a piece of wire, a nail, and bridge between the 2 wires. Even easier (I think), just pull off the plastic sleeves on the pigtail and touch the 2 wires to each other. That's the first test, along with pulling the connectors on the coolant temp sensor, to determine whether the fan motors are good. Because that switch is activated by high pressure in the condenser, it is also possible, in fact likely, that if the aux fans are not coming on, the refrigerant level may be too low to build adequate pressure to trigger the pressure switch. IIRC, the green pressure switch comes on at 16 bar and goes off at 12 bar. Or maybe it's 20 and 15, but it's somewhere in that range, and low refrigerant charge will keep it from attaining those sorts of pressures. Does you A/C have good cooling, or is it marginal? That's the place to start.

Thank you, I already established that I circled the wrong wires, and in fact it is the brown wires to the left of what I circled which needed to be jumped.

I did that, and the fan did come on.
The AC works fine I think, however so far it's not summer yet and it's hard to tell, but cold air was coming out.

I will have the gas checked/filled, and hoping that there isn't a leak somewhere

Incredible, I was looking for the same wires but I just can't find them in my 1990 W124.021 200E.

Guys,
I got the A/C unit regassed today, and the fan does come on.
However, it comes on every minute or so for about 5 seconds and then switches off.
Does that seem right?

Anyone know if the fan behavior I described in my previous post seems ok?