Well, it was in the mid 90s for a couple of days here in PA. Sure enough the Cool Harness V2 has the aux fans come on high speed at about 95 degrees and then they don’t turn off until you turn off the car. Too bad. In more normal temperatures, the aux fans never even come on at high speed, but in the very high heat it is on and never off.

The good news is that before the V2 install my car was doing pretty good with the heat. It seems that my fans running at low speed, from the AC pressure, keeps my car under 100 degrees with no problem. My aux fans were not responding to AC system pressure before, since my system was a bit low on charge. It still got cool in the car, but the charge was low. Now with a new full charge, the aux fans do come on low speed quite frequently and that seems to keep the car running cooler without going to the higher temperature that kicks in the high speed.

Now I am thinking that maybe the W124 would not run so hot if everyone had good AC systems with a full charge. The real weak link might be keeping a full charge in the AC system, since it seems everyone has issues with them. The AC system just leaks. Sooner or later it just happens. If you are lucky, it isn’t the evaporator. I am on my second leak in 10 years. The first was the expansion valve to receiver drier. This time it is the compressor.

Is it possible the Mercedes actually designed the car to stay cool in most normal situations by responding to AC pressure and that the high speed fan is really just a kind of emergency fail-safe kind of thing? It makes sense that you would have the AC on if it is hot, so why not depend on the AC? They also seem to have designed the car to use AC even in winter driving to control humidity. Maybe they just figured AC would always be on.

__________________
I just couldn't give up on my 1995 E320.

I think it might be like always going back to that same bad relationship with an ex girlfriend.
You feel you love them too much, or you are just too stupid to know any better.



Flickr slideshow of my 1995 E320
http://www.flickr.com/photos/24145497@N06/sets/72157616572140057/

Check the archives for a few articles I wrote on that exact scenerio..
No low fan is one of the most common, mis-diagnosed , causes of high coolant temp complaints.
Once the high thermal load caused by a/c passive heat exchange from condenser to radiator starts to creep on you , it's over...
I tell guys their problem with high coolant temps w/ac is caused by a slightly low refrigerent level and and they think I am crazy. [ until I top it off and the fan comes on at spec]
FIRST check for this coolant temp condition is LOW FAN , Problem is, the test used is they jumper the high side pressure switch and the fan comes On ..So,sure enough, they wrongly condemn the Switch.
It is almost [99%] always the refrig level, not the switch.
I have only seen 2 sw go bad ..and one was physically broken, the other had a short and ran the low fan all the time.
The best system is to run 2 wires off the drier pressure sw to a cabin sw [ on/off] that shunts the system so you can get a low fan on Demand manually. This is great also for towing. If the sw is OFF , the system just goes back to stock configuration b/c the sw is in parellel with the circuit.
The resistor bridge at the coolant temp sensor/thermistor for High fan does lower the cut-in of that sensors 105/107C value, but in doing so, it also lowers the CUT-OUT ..sometimes to the point of never turning off the fan. In other words , it has a differentail . With proper refrig/low fan operation [ and a cabin sw], you are controlling/checking thermal loads on the eng temps way before they gets to these higher temps.
And w/cabin sw , there is no cut-in/cut-out differential , so you don't have to worry about a HIGH fan on all that time [ not good for fan motor longevity or charging system]. Basically , I use the correct thermistor value as a coolant temp safety cut-in rather than trying to controll the engine temps with the High Fan. So, I keep that cut-in/cut-out on the high range, as it's main purpose is engine protection at higher than normal temps.
I also keep them at a higher cut-in so they turn back OFF after they have checked the condition ..that simple requires different R values. If one is in constant hot/Southern climates, then you may just have to use a lower cut-in of high fan for temp control, but that is another story..the large V/8 engine seem to benefit here also.
I actually use BOTH systems.
An added note to all this is that armed with this info, it is also easy for one to see that their a/c system is low on refrig simple by noticing a NO LOW Fan condition..you are in reality using the high side pressure sw as a monitor for rerig level.. [ just a casual observation]
The manual sw is not needed to control the temp if low fan is working, but it is a neat add-on for manual /over-ride control, as it can also be used without the a/c being ON [ like towing,etc].. I have always has a cabin sw on all my Benzs over the years , just in case that one time comes when I don't like the rising temp gauge staring at me in a traffic jam and I can't do a thing about it [ except throw that switch...

Thank you for your brilliant explanation. I am also feeling a little good about myself since I kind of figured it out.

The bad news is that now I think I just have to learn how to rig myself a switch. Do you think I could do it, even if I am not really much of a mechanic? My biggest accomplishment so far was that I was able to adjust my own vacuum modulator.

Another thing, since I have you here. If I have “dye all over my compressor”, as stated by my indy, is it likely that I need a new compressor and that is isn’t just a little leak from a connection. From reading on the forums, it sounds like the clutches go bad in the compressor and if I wait too long I may get all kinds of debris in my system as the compressor self destructs. I am thinking I should just go ahead and replace the compressor sooner rather than later. Does that make sense? Bye the way, I have a 1995 E320 with 105K miles. Also, it sounds like I should do the receiver drier and the expansion valve when they do the compressor. I did replace those two items about 4 or 5 years ago, but I read that you should always do the drier with the compressor.

Thanks again for your help. I just love these forums!

__________________
I just couldn't give up on my 1995 E320.

I think it might be like always going back to that same bad relationship with an ex girlfriend.
You feel you love them too much, or you are just too stupid to know any better.



Flickr slideshow of my 1995 E320
http://www.flickr.com/photos/24145497@N06/sets/72157616572140057/

>

This is a very simple wiring job.

Just get a regular ON/OFF toggle switch and a little bracket to mount it under the dash .
This sw will have 2 terminals..hook a wire to each terminal and run the wires [ I use lamp cord b/c the 2 wires are in the single cord, makes it easy and neat] thru the firewall somewhere and route them over to the switch at the drier . This sw is the one with the 2 pigtail wires on it ..your chassis has two white connectors on the end of this pigtail..just hook one wire to one of the 2 pigtail wires. and the other to the other pigtail wire at these white connectors..that's it, you are done.
This set-up uses all the original low fan circuitry of the stock system [ relay/fuse/resistor/etc], so there is no need to do any crazy elecrtonic additions..just the sw. Meaning it is a very safe , fused system.
When mounting the sw in the cabin, I mount them so when the sw in the ON position, the toggle lever is facing foward, as in the direction of travel of the car..that way you always know the sw is On or OFF from the toggle lever position.. Once the key is OFF, you will get no fan, regardless....
Once you have this additional manual control over your fans operation, Murfey's Law says you will never need it...

Reading this thread I get the impression that the two electric fans run independently of each other,,, is this true ? And if so which is high and which is low ? I always though the two started and stopped at the same time. Perhaps this is why the 400E is running a bit hot these days.

__________________
95 SL500 Smoke Silver, Parchment 64K
07 E350 4matic Station Wagon White 34K
02 E320 4Matic Silver/grey 80K
05 F150 Silver 44K

Your confusion is very common with these two different systems.

Fan Systems/Explaination :

The two fans are wired in parellel and ALWAYS work in unison.

There are TWO different circuits ,HIGH FAN and LOW FAN.

Each circuit is INDEPENDANT of each other , EXCEPT, they SHARE the same FAN MOTORS.

There is high fan relay, fuse , sensor circuit.

There is a low fan relay, fuse ,sensor , and dropping resistor [ Referred to as R15/ Pre-resistor.]

The a/c circuit can NEVER trigger a High fan, nor can the coolant temp circuit ever trigger a LOW fan..however , if the coolant circuit calls for high fan, that will over-ride a low fan demand from the a/c low fan circuit, resulting in high fan, regardless of a/c demand.

So, if one looks at a schematic, you will note that each of these independant circuits MEET at a COMMON terminal at/after the dropping resistor. [ the two wire side of the resistor]
That is the point in the circuit where either circuit feeds the FAN MOTORS. That is where they now share the fan motors, regarless of which circuit has a demand signal from it's circuits sensor [ Coolant temp sensor for high fan, a/c pressure sw/sensor for low fan.]
The low fan is accomplished by feeding 12v to the R15 resistor BEFORE this common terminal, thereby dropping the voltage to get a low fan RPM. Whereas , the High fan circuit by-passes thus R!15, allowing a full battery voltage to reach the fan motors, resulting in a HIGH fan RPM....
..so, two different circuits Sharing the same , parellel wired fan motors.
If you have a fan motor turning slower than the other , or not turning at all, the problem is NOT in either high/low fan circuits, it is a faulty FAN MOTOR .

I am not an expert, but from what I have read and seen with my car it seems that both fans run together. They can run at low speed or high speed, however, and they really go like crazy when they are on high speed. If they come on and your temperature is not over 100 degrees, then that is probably the low speed. If you ever get stuck in traffic on a hot day and your AC system is a bit low, so your fans don't come on at the low speed, then your temp may go up over 100 and then the fans will come on at high speed. I suppose they can also can come on at high speed without having low AC pressure, but I think it might take rather extreme conditions to get over 100 if your low speed fans are coming on with regularity due to the pressure in the AC system.

Others here are real experts, so they may chime in if I am getting too carried away with my newly acquired expertise on this matter.

Woops, I was too slow and a real expert answered while I was writing.

__________________
I just couldn't give up on my 1995 E320.

I think it might be like always going back to that same bad relationship with an ex girlfriend.
You feel you love them too much, or you are just too stupid to know any better.



Flickr slideshow of my 1995 E320
http://www.flickr.com/photos/24145497@N06/sets/72157616572140057/

You are now as Expert as I....

It is all in reading this Great Forum. All the info is right here.

Thanks once again for the great info Arthur,,,,, I sure wish you lived in Western Pa.

__________________
95 SL500 Smoke Silver, Parchment 64K
07 E350 4matic Station Wagon White 34K
02 E320 4Matic Silver/grey 80K
05 F150 Silver 44K

I did do a Gig once in Weastern Pa..at least I think that is W. Pa ??

York, Pa.
A Club right in the center of town, across from a Noodle Resturant..Very nice, but years ago, so my menory is cloudy on the exact Name of the Place [ prob not even there anymore.]
I do remember those long tunnels going through the mountains on the Pa Turnpike..What a road trip that was ...
Next stop from there was Erie , Pa...Completely different type town, if I remember correctly.

My wife was raised on a small dairy farm right outside of York Pa. She is still a great worker, thanks to that training on the dairy farm. She is a great cook too!

__________________
I just couldn't give up on my 1995 E320.

I think it might be like always going back to that same bad relationship with an ex girlfriend.
You feel you love them too much, or you are just too stupid to know any better.



Flickr slideshow of my 1995 E320
http://www.flickr.com/photos/24145497@N06/sets/72157616572140057/

York - East,,, Erie - West,,, about 100 miles north of Butler.

__________________
95 SL500 Smoke Silver, Parchment 64K
07 E350 4matic Station Wagon White 34K
02 E320 4Matic Silver/grey 80K
05 F150 Silver 44K

Another common failure is the resistor behind the driver side headlight. The resistor drops the voltage to create low fan speed. Have seen it queried more than a few times on the forum. As well, my low mileage/dealer maintained/Starmarked/owned by MB dealer management 124 came with a burned out resistor and no low speed fan operation. On this 1993 model the teltale clue was coolant temp rising to 105C, fans noisily engage, and coolant temp drops to ~95ish. Surprisingly, the A/C worked fine.

After replacement of the resistor and upgrading the wiring the low speed fans work great. The car sits on ~90C coolant temp and blows cold air all day long, no matter the outside temperature.

Since I know you're going to ask about the wiring upgrade. On the early 124 models a 2.5mm diameter wire supplied power to the resistor. For unknown reasons MB dropped this to 1.5mm on later models. The smaller wire tends to overheat and break near the resistor. Per a tip on this forum from Donnie, I replaced the entire wire from the low speed relay to the resistor and all has been well for several years.

- JimY

Yes , they dropped the wire size when they came out with the dual fans..but they under-estimated the current draw . They later changed the wire feed and also changed the fuse rating on low fan relay from 15 to 25 amp. [ the ones w/fuse on top of each relay]
Some guys in Tropical Climates take that same feed wire from the low relay to the R15 and use that to trigger another independent, higher amp circuit with another relay, which by-passes the R15 circuit altogether, allowing for High Fan for a/c condenser airflow. No need to change the wire from the 1.5 size b/c that now only feeds the coil side of the new relay. [ Low amps].
Never tried it, but I can see the advantage of a high fan for cond. airflow when one has the extreme thermal load conditions of Tropical type climates............................which lately, could be almost anywhere in the USA ...
Maybe we should just call that one the " Global Warming Modification TSB" ???
Here is the latest proto-type we are working on ..definate solution for
any Global Conditions , right into the next 10 years..

http://www.sl113.org/forums/uploaded/cees%20klumper/2005621181316_airco1.jpg

Got into the 400E tonite and found a VERY corroded,,, almost broken wire going to the resistor. Fixed the wire and as I ran the engine the low fans came on. I am sure the problem with the high temps was the wire to the resistor. Once again the forum saved me from a serious problem later on. MANY thanks to Arthur D. and Jim Y.
Now if I could only fix the idle surging on the 320,,,,

__________________
95 SL500 Smoke Silver, Parchment 64K
07 E350 4matic Station Wagon White 34K
02 E320 4Matic Silver/grey 80K
05 F150 Silver 44K