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  #1  
Old 04-12-2002, 08:47 PM
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auxillary fan/alignment w124

At what temperature is the auxillary fan supposed to come on? I was driving today with the A/C on, and at idle, the temp was creeping past 100*C. It seems kind of hot to me. I checked when I got home, and the aux fan wasn't on. Fuses appear fine too. The car just had a coolant flush last week, and a new radiator and water pump 6 months ago. I just bought the car last week, and am trying to spot any possible problems. Could this be one?
Also, the steering wheel is cocked to the left, and the car tends to pull to the right a little. At freeway speeds, the car sometimes feels a little unsteady for a mercedes (like the wind is pushing it sideways although there is no wind). The steering wheel also vibrates slightly at freeway speeds. Any thoughts?
Thanks a lot,

Matt
94 E320 138k
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  #2  
Old 04-12-2002, 08:53 PM
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In all likelyhood, you need to replace your "212" switch, which is located in the thermostat housing and turns your auxiliary fan on and off. It's a simple job and an inexpensive part.

Ron
German Star
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  #3  
Old 04-12-2002, 10:49 PM
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Matt,
Do a search on "aux fan" and you'll get lots of info. Several of us discussed this in depth last week. You will learn about the two speeds of the aux fans. Only the high speed is related to coolant temp, and even there it is set to come on about 107 degrees on most models, so you may not actually have an aux fan problem (though you may have an overheating problem).

ALso, the mechanical fan (driven by the engine) has a thermostatic clutch which often goes lame. Might also search on "fan clutch."
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'93 400E
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  #4  
Old 04-13-2002, 09:44 AM
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Question As far as ...

your vibration it could be that your tires need to be balanced and your car needs an alignment. While there, check all the suspension components. You can also change the steering shock, which is probably shot by now, if it is the original.
The "unsteady" feeling may be the rear suspension links.

As far as temperature, was the car doing this before you changed the coolant? Did you change the thermostat?
Do a search there is a lot of GOOD information on all these topics.
Good Lluck!
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  #5  
Old 04-13-2002, 02:04 PM
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As stated you have a two speed fan and the first speed is almost always on if its hot out and you are using the A/C. It comes on when the A/C gets to a certain pressure (which it will always do unless you are low on refrigerant).

There is no 212 switch on this guy. The A/C system turns the fan on for both refrigerant pressure and engine temp.
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  #6  
Old 04-13-2002, 02:19 PM
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Steve,

You said,
"As stated you have a two speed fan and the first speed is almost always on if its hot out and you are using the A/C. It comes on when the A/C gets to a certain pressure (which it will always do unless you are low on refrigerant). "


Is that true for most/all models? The reason I ask is my low speed fans rarely come on and stay on, regardless of ambient temp. THey'll come on for 10-30 seconds and then go off. I'm pretty sure I'm not too low on R134a since they've behaved this way for years and the AC has always worked well. From what you say, sounds like they should be running fairly continuously. Might I have a bad pressure switch? How is it tested -- I assume by hooking up AC pressure gauges and seeing if the switch closes when the AC pressure gets to the set point?
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  #7  
Old 04-13-2002, 02:46 PM
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The magic words in SBs reply are "if it's hot out".

It is quite possible to have a/c operation at cool ambient temp/low humidity with a full charge of refrigerent and the system not calling for aux. fan.
The system design is for the fan to come into play when the system is being taxed/burdened. ie- when it HOT.
[ HVAC term is "High Thermal Load" ] , -but hot is fine for us.
With a high demand , the high side pressure increases and
can be kept in check by moving more air accross the condensor.
That's when and what the aux fan does.
And when it is hot out , these conditions are met and the fan is called for...
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  #8  
Old 04-13-2002, 03:11 PM
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Sorry, I suppose my experience is clouded by the fact that if there is a higher heat/humidity than Baton Rouge, then it is in Gainesville FL.

We were finishing a compressor install Friday evening on a 91 300E that had no A/C when it came in. No problem promising the job at the end of day. Well its 5:30 and we've got it 75% full and the pressure is bumping over 400psi as I walk up to the tech to check progress. NO AUX FAN. He heads for the test light and I head for the parts dept to get the blower resistor. Had it to him as he was sliding out the dead one. High side stabilizes at 320psi with the fan and its out the door.

No wonder the shaft seal blew on the old compressor.
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  #9  
Old 04-13-2002, 07:06 PM
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Helpful info from both of you gentlemen --

I had the low-speed resistor replaced last year. Good to be reminded that the low speed fan is really there to protect the compressor from those high pressures. . .
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'93 400E
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  #10  
Old 04-13-2002, 08:45 PM
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update

When I bought the car, I drove it 600 miles, mostly at night, and the temp. seemed fine (about 80-85). Last night, I was sitting in a drive-thru line for about 10 minutes and my temp was again just above 100 degrees C. The temp outside was 63F, low humidity, and my air conditioner was off. Seems like it was running hot to me. Today I was driving around downtown and the temperature outside was about 85F and the car temp was running about 95-102C. I had the A/C on, but the aux. fan wasn't running at all. I guess I'm going to take it in next week to get looked at, but was just wondering if I'm looking at an aux. fan problem, A/C problem (refrigerant is a little low, I think), or just an overheating problem. How much would fixing each cost?
Thanks,
Matt

94 E320 138k
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  #11  
Old 04-13-2002, 09:13 PM
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Before you take it anywhere check the aux fan relay fuse. On my '95 model it is behind the regular fuse box underneath the black plastic cover. You have to remove phillips head screws to remove the cover. Check the fuses plugged into the top of the relays in there.

There was a thread talking about how you can run a slightly higher amperage fuse without running into any problems.
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  #12  
Old 04-14-2002, 12:01 AM
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thanks...

Thanks Jim,
I checked the fuses, and the 15 was burned out. I replaced it and the aux. fan came on when it was supposed to. The car was running 90 and below now. It didn't hit 100 at all, and I was driving stop and go. I'll test it out tomorrow to see if it can handle the mid-day heat, but I don't think I'll have any problems. My last question is why this fuse would have blown?? I just had the wiring harness, a coolant hose, and the thermostat replaced last week...could that be related?
Thanks again,
Matt

94 E320 138k
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  #13  
Old 04-14-2002, 09:57 AM
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Somewhere posted on this site it discusses upgrading the fuse to a little higher amperage. That is what you are eventually going to want to put in there. I don't remember the higher amperage rating but next time the cover is off of mine I will make note of it.
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Last edited by engatwork; 04-14-2002 at 10:24 AM.
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  #14  
Old 04-14-2002, 10:24 AM
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Benz OKs a 20 now. The original fatiques as the fan can draw around 17 amps and as high as 25 momentarily at start up.
I have seen 25s used , but I think 20 is fine as they have a
start spike tolerence.
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  #15  
Old 04-14-2002, 09:23 PM
PA_Joe_300E
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87 300e auxiliary fan

Can anyone tell me the location of the components for checking the auxiliary fan. I don't think it come on at all. Where is the relay located? The a/c cut out under extreme conditions.
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