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  #1  
Old 07-29-2003, 11:41 PM
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Auxiliary Fan Question

560sl, the my auxiliary fan does not operate properly. I can jump it so I know the fan is good.

The electrical connects to the filter drier via a plastic sleeve. Can I disconnect the plastic connection (green in this case) or is it integral to the filter drier and not replaceable by itself. In other words, if I mess with it, will all the freon escape?

Thanks.

J. Boggs
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  #2  
Old 07-30-2003, 12:01 AM
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Location: Florida / N.H.
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The sw can be replaced , but you loose the freon ..
However, the sw is a pressure activated trip and it is more likely that your a/c system is short of freon. This results in the high side pressure never getting to the sw cut-in spec....
Look at the drier sight glass for freon charge level before changing the sw...or test high side pressure w/gauges..
You have fan when jumping sw. so you know the electicals of the fan circuit are fine [ with the exception of the sw circuit]
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  #3  
Old 07-30-2003, 12:14 AM
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Thanks,.

I just had the a/c serviced and pressures are good. Bad switch I guess?

thanks.

J. Boggs
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  #4  
Old 07-30-2003, 12:41 AM
azhari
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Use a multimeter to check the switch contacts when a/c is on (multimeter set to check resistance).

If the switch contacts do not close at all after the a/c has been on for a couple of minutes (no resistance reading), you can be sure the switch is the problem.

My 2 cents...
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  #5  
Old 07-30-2003, 09:52 AM
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< >>

The only way to truely check the sw is with gauges on the High side for sw spec comparision..
There are times when the fan is not called for [ low thermal load conditions , ie -low temp/humidity] , so do not expect a fan under these conditions.
The fan is there as an AID to high head pressure of the condensor [ a/c high-side] and simply comes to the rescue
when more airflow is needed..usually at stop/idle on hot ambient days. Once the car is moving , the air now crossing the condensor will limit the high side pressure and the sw will open and turn the AUX fan OFF...
So, one can see, if the freon level is not COMPLETELY charged, the system will never reach a high side sw cut-in spec for aux fan...A trained eye can see this in the eye-sight and a trained hand can feel the temp on the condensor in and out lines , but for exact sw cut-in/out pressure comparisions, gauges are your next step for proper diagnosis..
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  #6  
Old 07-30-2003, 10:05 AM
moedip
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J. Boggs
I just finished with temp problems on my 560 sel. Last month I thought I had problems with my aux fans not coming on and engine temp running about 100 - 103C with a/c on on days when it was 90-95F with a/c on on the highway. Like every one else with similar threads I thought there was an aux fan turn on problem. Then Murphy struck this month. I was out for a Sunday drive - stopped to get gas and noticed a wisp of steam from under the hood while tanking up. I started the car and - Bang - antifreeze all over the place. The dreaded broken rad neck syndrome. Patched the rad and limped home with 5 gallons of water in the back seat - adding as required. I replaced the rad and took the car for a spin - temps were about 110C with a/c on on the highway. Got home and let the engine cool. Then started it with hood up and watched the temp guage. That's when I found the book is correct. The aux fan came on ONLY when the engine temp hit 107C and ran until the temp dropped to 100C. So what I learned was that the aux fans are only for backup to keep engine temps below 107C. Why was my engine running hot with a new rad? - Murphy again! The viscous clutch was not engaging the fan - it just lazily turned as if at idle. The clutch was new 3 years ago and only had 7000 miles on it. I put a new one in - and Presto - engine temps now staying at 85C to a max of 97C under high outdoor temps on highway with a/c on. If your engine temps are under 100C - from what I have learned - don't expect to see your aux fan come on. It's a good thing I LOVE my old girl - she has cost me a lot of $$$$$ this month - and she still is beautiful! and yes - I am talking about the car - not my wife!!!:p :p :p :p
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  #7  
Old 07-30-2003, 12:13 PM
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Fan Confusion again ??

Ok , this is all archived, but this is a good time to run it again...

The AUX fan confusion on most AUX. fan post seems to stem from the tricky part of the FAN circuits and applications..this tricky part is the fact that there are 2 [ yes-two] fan circuits , but they SHARE the SAME fan motor/s....
So, without getting into tech details, here are some simple things to observe that will help all in a better understanding of the whos/whats of the AUX fan/s...

The main [High speed] aux fan is there to AID the ENGINE cooling system in the event that the coolant temps start to get in a DANGER ZONE...this usually occures under extreme conditions
and is normal...[that is why they have the cut-in temp so high].
Under NORMAL conditions , this AUX is not needed and the sensors do not call for it.....

The low speed fan is there to aid the A/C systems high-side pressure from getting so high that it is in a DANGER ZONE..[ along with decreased cooling ability]
If the systems pressures get too high , a sensor will shut down the a/c... but before that happens , the sw on the drier sees this pressure increase and it completes the circuit for LOW fan to add
more air-flow accross the condensor to AID the a/c systems cooling ability and keep the pressure in check..
So, what we have here is two INDIVIDUAL fan circuits that accomplish two different functions, but they do it with the SAME fan MOTOR..
Can we have an aux. fan come on without seeing high engine temps ??
..OF COURSE... it will come on when the a/c system tells it that the high-side pressure is getting up there..nothing to do with engine coolant temps.[this a/c will be low fan, by the way]
Or , can we see a aux fan come on when engine temps start getting up around 105-110 , even with the a/c OFF ???
... Sure.... the coolant temp sensor will activate the Coolant Temp AUX fan CIRCUIT and turn on the AUX fan to AID the radiator with more air to check the high engine temp [ this will be high fan].. This will still be The SAME FAN MOTOR..
So, as you can see , when checking your aux fans, you want to know which CIRCUIT you are checking, because the two circuits have there own relays, sensors, fuses, etc... the only common part they share is the FANS themselves..and that is the tricky part that makes for the confusion..
**** NOTE... the reason TECHS jumper the a/c drier sw to look for fan is simply because that is an easy place to jumper for a quick test to verify that the fan motors and feed fuses, wiring, etc are intact ..it is a priliminary test to aid the tech in elimination of parts in short order....it reality, it does not mean that one needs a drier sw., and it has nothing to do with the engine coolant side of ther circuit [ high fan], except to tell that the fan motors are
well...
I guess an easy thing to remeber is...HIGH FAN comes on with HIGH engine coolant temps..
LOW fan comes on when a/c system is cooling [low temp] and the ambient temps are up in the high thermal load conditions to call for aux fan help....
There was a post where one noted that the low fan was on for a few min. at idle and then it switched to high fan...
How come ??
Simple.. the a/c was on and the low fan was being called for by the a/c high side pressure sw [ low fan]. As the car now had a/c on and was at idle a few more min., the coolant temp started to go up , so the engine coolant temp sensor tripped to keep the coolant in check..
So, what we have seen here is BOTH SYSTEMS in operation at the SAME TIME , with the SAME FAN/S.. both systems calling for assistance and both reacting, with the high speed taking prefernce, of course...
A side point here is the fact that if your a/c high side LOW fan circuit is not working properly [ fuse,relay, resistor, etc.], you can still have a/c , BUT, [ note big but] the condensor will run hotter than normal and this will INDIRECTLY affect the Engine COOLANT
temps because the condensor is in front of the radiator and that will affect the radiators efficiency [ this is a passive heat exchange, but often overlooked when one is diagnosing engine temp slighly higher than normal, but not high enough to trip coolant temp sensor] this will be noted only with a/c on and more likely at slow/stand-still conditions..
...Meaning it is important for both fan systems/circuits to be operational, even though they are independant, circuit wise.

I knew this had to get a little techie, but hope it helps anyone wanting some further understanding...and only on this system design...

*An Added PS on Fan SPEEDS.
How does the aux fan get the high/low fan difference with the
same fan motor???
Simple... there is a resistor [voltage dropping] in the a/c fan circuit to lower the speed ...[ this is the resistor you see mentioned in many fan post.... they burn up from high heat /amp draw]...this resistor is in series with the a/c fan relay and the fan motor.
BUT, in the engine temp circuit , that fan relay feed bye-passes this resistor and give full battery voltage to the fan motor/s...
thus, HIGH fan...[ same fan, different feed]

Last edited by Arthur Dalton; 07-30-2003 at 12:42 PM.
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  #8  
Old 07-30-2003, 10:05 PM
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Thanks for the detailed explanation

I was merely stuck in heavy traffic the other day and the temp guage started to get close to redlining (I turned the A/C off), but before it redlined, traffic moved and the crisis was solved. I was just wondering if I had sat there much longer would the fan have come on.

Thanks.

J. Boggs
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  #9  
Old 07-30-2003, 10:40 PM
azhari
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Arthur

That was a very good post!

A side point here is the fact that if your a/c high side LOW fan circuit is not working properly [ fuse,relay, resistor, etc.], you can still have a/c , BUT, [ note big but] the condensor will run hotter than normal and this will INDIRECTLY affect the Engine COOLANT
temps because the condensor is in front of the radiator and that will affect the radiators efficiency [ this is a passive heat exchange, but often overlooked when one is diagnosing engine temp slighly higher than normal, but not high enough to trip coolant temp sensor] this will be noted only with a/c on and more likely at slow/stand-still conditions.


I'm very familiar with overheating solutions for 124s/201s with respect to the clutch/aux fans but your post really filled in some gaps in my head with regards to the a/c system in connection to the cooling system!

Btw, did you get my email abt the schematic?

Thanks.
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  #10  
Old 07-30-2003, 11:07 PM
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Location: Florida / N.H.
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aux fan schematic ?
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