I think your last statement is what they had in mind; since they call it "climate-control", I think they wanted you to keep it on set for "70degs" (or whatever temp makes you happy) and then the fans will take care of keeping your engine cool. Since the A/C will be on, the fans will come on when needed.

Of course, you need to keep your A/C operational . . . but using your "ears", you can tell when something isn't correct . . . if the fans don't come on "low", on a HOT day, then something is wrong. *

If you ever "forget" what the key trigger points are for each separate mode operation, go to MENU#18 and look at the table, called "Aux Fans Activation", in the middle of the page. All the key 'numbers' are there. . .

* You can check the A/C's operational parameters by accessing the info via the control panel. Follow MENU# 15 to read-out these parameters esp "5" (a/c evap temp) and "7" (a/c compressor pressure). The latter will tell all . . . high vent temp or very low pressure means a low charge.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Hi Jim,

It is great to have you chime in on this. My friend's W210 has that kind of access to all kinds of information. The W124 does not have that available, as far as I know.

I also have a friend that wants to play with a slightly different resistor in your cool harness, to see if he can get the high-speed aux fan function to turn off at normal driving temperature after it kicks in. It may come on just a bit higher than 95 degrees, but still just short of say 100, so that the fans will still prevent excessive heat, but will also turn off when the car gets back down to 90 degrees. Right now, on a very hot day, my high-speed fans do not turn off after they come on with the cool harness V2. I think I still prefer that to seeing 105 degrees, but I also think I am interested in maybe just a slight tweaking of your cool harness. Maybe a resistor that kicks in a 97 or 98 degrees would let the things turn off. As I remember, you had a 97-degree cool harness in the old version. Did that one allow for the fans to turn back off on a very hot day, so it cycled more like with the stock system?

Thanks for the information Jim,

Ken

__________________
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 KEY wording here is : "..on a HOT day".

Aux fan is just that....an aux added fan to AID the system with increased air-flow when the sensors detect a "Higher than normal Thermal Load".
A/c is used in winters to aid in clearing windshield of humidity, but you will never see a low fan when it is doing so... b/c you have NO High Thermal Load.
Car travelling down the road at 45 MPH, a/c On , no aux low fan.. b/c it is not needed... NO high thermal load b/c travelling vehicle has plenty of airflow to keep condenser pressure in check. But come to a stop light or slow traffic and On comes fan..b/c of rise in Thermal load and Sensor Demand for more air-flow..
So, the word HOT here is the trick, coupled with low airflow..
Do not expect to see your low fan activated on a cool day just b/c your a/c is ON..it only comes on with Thermal Load Demand .. it is ONLY an aux airflow aid device.. mostly activated at idle, car at rest, hot conditions...and it is actually possible in cooler climates to never come on .

So, how can you actually determine if the low speed fans are doing it's job? With the car stoped and a/c on, you can see the fans runnig but when driving how can you tell if they did turned on at the right moment? I can actually hear when the hi speed fans turn on when temperature is like 110 or something but, can you hear the low speed fans when driving?

And the other question is, how can you test the resistor?

Thanks for this great info.

__________________
-----------------
Juan
1995 E320 Sedan
2008 Ford Escape
RC Helicopter

<>

The correct Moment is if the high side pressure switch is calling for the aid of aux fan..if there is a very high thermal load , they come on, if not, they don't..so, if they come on at idle w/ac on on a hot day, they are fine.
When the car is moving, they may come on or may not come on..that is dependent on demand of high side pressure, which is determined by the intensity of thermal load. If they are called for to check pressure and they do not come on ,then the high side will get to a dangerous pressure and the compressor cut-out pressure switch will deactivate the compressor and you will have no a/c.
All fan activation is on pressure demand..the pressure sw does not know if the car is moving, what the temp are , or any other variable..it only knows that SOMETHING is making the high side pressure get out of spec, so it comes on to bring that pressure back to efficient working condition. [ that is what the airflow does..it drops the condensers pressure.]

The R15 resstor can be checked with an ohm meter or a test lamp on each side of the circuit..if you have low fan, you do not have a bad resistor..high fan does not use the R15.

Now I understand and know that my E320 has hi and low fans working ok.

thanks again Arthur.

__________________
-----------------
Juan
1995 E320 Sedan
2008 Ford Escape
RC Helicopter

I have a related question.

What is the correct way to put additional refrigerant into a 1998 air condition system? I believe this is R134.

I always tell everyone I am not an expert before I say anything, so please keep that in mind.

I was told that the correct way to add refrigerant is to pull a vacuum for some period of time and then add a specific measured amount, by weight, of the correct refrigerant. I was also told that measuring pressures, high or low pressure side, is not an accurate way to determine how much to add. I was told that the low side pressure is an especially poor diagnostic, which is what most DIYers do in their driveway.

For me, it is only about $60.00 to have it done correctly at my Indy.

__________________
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/

I guess I picked a bad example for '95 owners but for the newer models ('96 and on), you can read the A/C operational parameters from the dash controller.

Press "REST" for 8 secs or until the display changes to "1" in the left window and "TEMP" in the right window.

Press left "AUTO" to advance to next step; press right "AUTO" to decrease one step.
Step #5 is evap temperature and #7 is compressor pressure in BAR. (14.7psi = 1 bar). So if you 'sort-of' remember the "Aux Fan Activation" tables, then you can tell by the pressure where the aux fans state should be.

Yesterday, I took a '02 E320 for a ride and pressed "REST"; sure enough the operational parameters read out. . it's a/c evap was 35F. . w/ the compressor at 15bar. 35F is . . . . cold!!

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

It was great to stay cool in the traffic jam on the NJ Tpk yesterday on my home from New Brunswick NJ. There is always a jam where the truck and car routes converge. Usually I had to sit and watch my temperature climb to about 105 degrees before my high speed fans would kick in. Not anymore, since I have the Cool Harness V2! The fans do seem to stay on, once they are triggered at 95 degrees, but that seems much better than waiting to see 105 degrees. The reality is that if it is a hot day, the fans would have had to come back on again anyway. I suppose it is OK that they just stay on. I can't hear the fans at 80 miles an hour anyway. I think I would rather pay to replace my fan motors some day than run my car back and forth up to 105 degrees. Maybe now my head gasket leak won't get worse too fast. The car never went over 95 degrees. It was usually about 87 degrees when moving, just as it is supposed to be.

Anyway, I am a happy customer with my Cool harness V2.

Thank you JimF

__________________
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/

Going back to Arthur's explanation of the HIGH and LOW fan systems, imagine this scenario:

- You have the manual switch in place but it is in the OFF position.
- Your A/C is OFF.
- The car heats up in stop and go traffic.

Will the HIGH fans still kick in when the car gets hot enough (105 degrees, I presume)? It would make sense since the HIGH and LOW fans are on different circuits, however, I am not sure if installing the manual switch puts it on the LOW fan circuit only.

Also, since the Cool Harness was also mentioned:

Does the original Cool Harness have the same problem as the V2 -- keeping the fans on HIGH once they are on? Is this a consistent problem with Cool Harness users or an isolated incident?

I am interested in applying both changes to my '89 190E 2.6 which has a dead A/C (leaky evap).

The hysterisis for the Aux Fan ckt is around 5 degs C; so if it goes on at 100C it should go off at 95C. Those MBs with multiple fan speeds have a slightly larger hysterisis value (on=115C; off=107C) at higher engine temps. All of this info is in MENU#18 in the "Aux Fans Activation".

If your car has dead A/C then it shouldn't get to 100+C; suggest that you follow the steps in MENU#17 in the "agua" colored table. The 5 steps should lower the engine temp so that the fans won't run all the time.

My car with A/C in 95F w/ 80% RH, doesn't go above 95C. On the highway, it's under 90C. So the A/F are off.

If the A/Fs don't go off, it's b/c the engine temp doesn't lower when the fans turn on, indicating something isn't right. The Cool Harness doesn't KEEP them on, your engine temperature does!

Also the original Cool Harness comes in three (3) ranges as shown on the CH table. I use the CH-92 but many prefer the CH-95 and/or CH-98. The numbers represent the trigger point for A/F cutin.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Jim, thank you for the clarification. It makes sense now.

My car also stays below 90C on the highway. In stop and go traffic without A/C and roughly 95F ambient temperature, I have seen the auxiliary fans come on several times during the last 2 weeks or so. It looks like they engage at around 105-110C. It is a rare occurrence and the car cools down quickly with the fans on, but having them engage earlier will give me some extra peace of mind. CH-92 would be my choice as well.


Update from 8/26/07:

I installed the Cool Harness today, went with a CH-95 instead. It works flawlessly. Fans engage at 95C and go off at around 87C. This is awesome!

Guys

I don't mean to takeover this thread, but I have been reading quite a few since my temp gauge went to 120+ in traffic a couple of days ago (ambient temp was 32C or about 95F). I tried to get the fans to come on by turning on the A/C but they refused, so I managed to lower it by turning down some side streets & getting some air through the radiator.

A/C works well & the belt driven fan clutch was renewed last year & seems to be working OK.

I've tried to do some tests and so far today (35C) I have had 1 fan come on high at about 95-100C with the A/C on a short trip (right side looking at it from the front - your driver side).

Later I removed the Temp guage connector (which looked a bit beaten up) and the same fan came on high, but nothing from the other one.

When I bridged the plug I heard relays switching near the fusebox & near the A/C drier but no Low fan came on - in either of the fans.

I also tried bridging the each side of the Low fan resistor with 12v - but nothing happened with either side fan. Though I may not have done this correctly?

Does this mean -
I have at least 1 fan that's dodgy;
I possibly have a Resistor that's stuffed;
Possible other problems...

Any help greatfully accepted.

PS - something else I was wondering is that when all of the R12 was replaced with R134a a few years back, how does this affect the psi readings from the A/C for the Low speed fan? Are they close enough?

Cheers

Stu

Is this a double post?

__________________
A Dalton