Question about Mercedes-Benz S-Class

8 Answers

Dear Technical Expert, Please kindly help me to find out what is the root cause of the high temperature(1994-1995 Mercedes Benz 500SEL engine 119970) when the vehicle is not moving ie when engine idling during waiting(in the case of traffic jam). Status: Either with air-conditioning unit on or off. When waiting, the temperature indicator keep on rising from 80 deg C to 115 deg C and the 2 Aux Fans not kick in between 80-90 deg C at low speed. However when the regrigerant pressure reaches 300# it automatically activates the 2 Aux fans and run at high speed. It seems that the Aux fan does not function at low speed!! Whenever the vehicle is on the move(normal rod) the temperature starts to drop to 85-95deg C(assume this is norm range). Please kindly advise if the problem is due to: ballast resistor(stage 1); aux fan resistor(stage 2) and aux fan relay? If anyone of it does, vide location drawings for these related components. Thank you very much. Best regards.

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  • virgo8bn Feb 01, 2010

    Dear Technical Expert,
    Please kindly help me to find out what is the root cause of the high temperature(1994-1995 Mercedes Benz 500SEL engine 119970) when the vehicle is not moving with engine on ie when engine idling during waiting(in the case of traffic jam).
    Status: Either with air-conditioning unit on or off. When waiting, the temperature indicator keep on rising from 80 deg C to 115 deg C and the 2 Aux Fans not kick in between 80-90 deg C (stage 1 low speed). However when the refrigerant pressure reaches 300# it automatically activates the 2 Aux fans(on and off) and run at high speed and cools down the engine temperature a bit. It seems that the Aux fan(stage 1) does not function for the low speed!
    Is this model equipped with 2 aux fan speed(low and high)for the engine temperature control? If there is, where can I find the locations for: (a) ballast resistor(stage 1) the (b) aux fan resistor(stage 2) and the (c) aux fan relay??
    Thank you

  • virgo8bn Feb 01, 2010

    Unable to get an ecopy of the said service manual as highlighted.
    Please help again exactly where to retrieve or otherwise sent over as
    attachment to me hopefully to ease troubleshooting. Thank you.

  • virgo8bn Feb 01, 2010

    Dear jambanshee 74,

    The problem is the aux fan does not function(low speed) when
    temperature reaches >80 deg C. Can you please clarify
    whether the aux fan function directly from the coolant
    temperature sensor(at manifold) detection or through some kind of a
    program(D/I converter) or swiching via aux fan relay?

    Can you help to get an ecopy of the schematic control/wiring diagram and component location drawing?

    Thank you.



  • virgo8bn Feb 01, 2010

    Can anyone help perhaps with auto air/con expertise in additon to mechanical knowledge(read below);
    Dear Technical Expert,
    Please kindly help me to find out what is the root cause of the high temperature(1994-1995 Mercedes Benz 500SEL engine 119970(Chassis 140051)) when the vehicle is not moving with engine on ie when engine idling during waiting(in the case of traffic jam).
    Status: Either with air-conditioning unit on or off. When waiting, the temperature indicator keep on rising from 80 deg C to 115 deg C and the 2 Aux Fans not kick in between 80-90 deg C (stage 1 low speed). However when the refrigerant pressure reaches 300# it automatically activates the 2 Aux fans(on and off) and run at high speed and cools down the engine temperature a bit. It seems that the Aux fan(stage 1) does not function for the low speed!
    Is this model equipped(or programmed) with 2 aux fan speed(low and high) for the engine temperature control? If there is, where can I find the locations for: (a) ballast resistor(stage 1) the (b) aux fan resistor(stage 2) and the (c) aux fan relay??
    Remark: The fan clutch has been checked by mechanic and is within acceptable speed and showed me by example a s500(coupe) during engine idling the temperature slowly reaches 80 deg C. Whenever at/exceeds 85 deg C(stage 1 temperature setting or programmed??), the aux fan switched on continuously run at low speed and stops when the temperature drops below 85. In addition whenever aircon is on, if only refrigerant pressure reaches 300#(A/C pressure switch) the aux fan start to run at high speed(on) and off when pressure drops below 300# irrelevant to engine coolant temperature so the engine coolant temperature is maintained around/below 85 deg C(assumed norm) by switching on the aux fan at low speed. This scenario has been observed from the typical s500 coupe(assume 500SEL same concept).
    The other assumptions were: Thermostat operative and radiator is in good condition

    Can anyone/expertise help to get an ecopy of the electrical control schematic/wiring diagram related to this problem for clarification?
    Thank you very much

  • virgo8bn Feb 01, 2010

    I do understand that the fan clutch is thermally sensitive. By the way,
    is there any way discuss this issue with aircon expertise why the aux
    fan does not function for stage 1 low speed in the first place as the
    coolant temperature increases beyond 80 deg C?.

    Thank you.



  • virgo8bn Feb 02, 2010

    Dear ZJLLimited Expertise,

    I have read through your comments and need to identify some of the(not
    obvious) exact components locations as referred to your
    suggestion of the checking list with 13 items/components.

    (a) 9 Inspect > Relay - Raditor Cooling Fan Motor > Faulty Cooling Fan
    Relay
    .

    (b) 11 Inspect > Cooling Fan Switch - Raditor > Faulty Raditor Cooling
    Fan Sensor/Switch
    .

    Please kindly provide further whereabout/locations of the 2
    or 3 components(underlined under (a) and (b)-see above) details to
    identify components.Note: Assume that this may need consultation with
    auto (M/Benz) aircon experts!

    Your urgent feedback is appreciated.

    Thank you.



  • virgo8bn Feb 02, 2010

    Thanks for the info. Have seen my latest comments?



    Dear ZJLLimited Expertise,

    I have read through your comments and need to identify some of the(not obvious)
    exact components locations as referred to your suggestion of the checking
    list with 13 items/components
    .

    (a) 9 Inspect > Relay - Raditor Cooling Fan
    Motor > Faulty Cooling Fan Relay.

    (b) 11 Inspect > Cooling Fan
    Switch - Raditor > Faulty Raditor Cooling Fan Sensor/Switch.

    Please kindly provide further
    whereabout/locations of the 2 or 3 components(underlined under (a) and (b)-see
    above) details to identify components.Note: Assume that this may need
    consultation with auto (M/Benz) aircon experts!

    Your urgent feedback is appreciated.

    Thank you.



    -------

    Also in addition enquiry forwarded to others FixYa expert(see below).



    Dear Charlymonty Expertise,

    I am confused when you stated the following components:

    Please clarify

    (a) The externally mounted resistor near the coil is the distributor resistor.

    What is the actual component referred/called in M/Benz(ballast resistor)?

    it appears that the ballast resistor terminal is located within the housing
    (casing) of the starter solenoid .



    Remark: Also refer comments from Jambanshee:one of Fixya expertise(see
    belo):-



    ----------



    Additional query to Jambanshee:-







    Thanks for the briefs however I need further confirmation
    wrt components referred in your comments.

    (1) When you pulled the temp sensor from the engine. What/which
    do you mean? Is it the CIS injection 4 pins terminals coolant temperature
    sensor or A/con ACC temp sensor(2 pin)??.

    Remark: Fyi, Mechanic has tried to pulled out the A/con ACC temp sensor(TR100,
    not sure what is the temp setting; 130 deg C for emergency/fail safe?) and the
    aux fan run at high speed though!

    (2) Note: in 95 mercedes instituted a
    running change on the fan resistor assembly. They made it a 2 speed operation
    (low/high) and replaced the ceramic resistor assembly with a single low speed
    encapsulated resistor. It appears as a verticle rod approx 3/8 in diameter and
    4 inches long sitting front of the AC condensor/radiator.
    The
    vertical rod(similar-black) as mentioned can be found at location however
    external looks good(no sign of burning/charred). In order to measure
    resistance(what is the norm Ohm value?) by VOM where can I find the
    terminals/connection that leads to?

    (3) You also states that the relay could be faulty. "a break in the low speed circuit, probably either a relay or
    a resistor problem"
    Where can I find this relay(you mean the Aux
    fan relay?).

    (4) "calibrate coolant temperature with a digiital
    thermometer
    " mechanic has compare the reading by laser digital
    temp reader, acceptable!

    (5) As you have stated that the 3/8"Dia x4" long resistor may have
    been the replacement for the ceramic resistor. Do you mean as a replacement for
    the combination of the ballast and aux fan rsistors?? If ceramic resistors to
    be installed/used(back to basic original design), where are these component
    supposed to be located?

    Please kindly clarify the above ASAP.

    Thank you.






  • virgo8bn Feb 02, 2010

    Additional enquiry:



    Dear Charlymonty Expertise,

    I am confused when you stated the following components:

    Please clarify

    (a) The externally mounted resistor near the coil is the distributor resistor.

    What is the actual component referred/called in M/Benz(ballast resistor)?

    it appears that the ballast resistor terminal is located within the housing
    (casing) of the starter solenoid .



    Remark: Also refer comments from Jambanshee:one of Fixya expertise(see
    below):-



    -
    On the aux fan side, I have been there and can
    add some comments. When you pulled the temp sensor from the engine, the fans
    should go to high speed. This is a fail-safe mechanism in case a temp sensor
    wire gets broken or loose. This indicates the high speed fan circuit is ok. The
    fans should come on at low speed at any temp when you initially turn on the
    A/C. (they may cycle on and off as well). If that is not happening you probably
    have a break in the low speed circuit, probably either a relay or a resistor
    problem



    Note: in 95 mercedes instituted a running change on the fan
    resistor assembly. They made it a 2 speed operation (low/high) and replaced the
    ceramic resistor assembly with a single low speed encapsulated resistor. It
    appears as a verticle rod approx 3/8 in diameter and 4 inches long sitting
    front of the AC condensor/radiator. This was a mistake by Mercedes since the
    resistor (rod) burns out prematurely. The affects low speed operation. The
    Mercedes parts instructions call for the unit to be replaced by the old ceramic
    resistor assembly. You can do the checks with a simple VOM.



    If the resistor wiring is ok and the relay checks out, you likely have a
    defective climate control. Changing the value of the resistor values to fool
    the climate control seems like a workable solution. It may shift over time,
    however. Also, don't trust the temp guage. Always calibrate coolant temperature
    with a digiital thermometer.






    Additional query to Jambanshee:-







    Thanks for the briefs however I need further confirmation
    wrt components referred in your comments.

    (1) When you pulled the temp sensor from the engine. What/which
    do you mean? Is it the CIS injection 4 pins terminals coolant temperature
    sensor or A/con ACC temp sensor(2 pin)??.

    Remark: Fyi, Mechanic has tried to pulled out the A/con ACC temp sensor(TR100,
    not sure what is the temp setting; 130 deg C for emergency/fail safe?) and the
    aux fan run at high speed though!

    (2) Note: in 95 mercedes instituted a
    running change on the fan resistor assembly. They made it a 2 speed operation
    (low/high) and replaced the ceramic resistor assembly with a single low speed
    encapsulated resistor. It appears as a verticle rod approx 3/8 in diameter and
    4 inches long sitting front of the AC condensor/radiator.
    The
    vertical rod(similar-black) as mentioned can be found at location however
    external looks good(no sign of burning/charred). In order to measure
    resistance(what is the norm Ohm value?) by VOM where can I find the
    terminals/connection that leads to?

    (3) You also states that the relay could be faulty. "a break in the low speed circuit, probably either a relay or
    a resistor problem"
    Where can I find this relay(you mean the Aux
    fan relay?).

    (4) As you have stated that the 3/8"Dia x4" long resistor may have
    been the replacement for the ceramic resistor. Do you mean as a replacement for
    the combination of the ballast and aux fan rsistors?? If ceramic resistors to
    be installed/used(back to basic original design), where are these component
    supposed to be located?

    Please kindly clarify the above ASAP.

    Thank you.




  • virgo8bn Feb 02, 2010

    Dear Charlymonty(Experts),



    Thanks for the info.

    For your further information, it has been observed that the aux fan(2)
    kicks in either by the refrigerant pressure reaches 300# or 115 deg C
    from the engine coolant temperature sensor(ECT- B11/2, CIS injection 4
    pin terminals color code Black). Also the CTS installed(A/c ACC
    coolant temperature sensor-B10/8, Blue air conditioning "OFF" Emergency
    switch 130deg C!) Ohmic resistance varies(measured @ ambient from 4kOhm
    to about 365 Ohm at 100deg C boiling water).

    From various sources, it has been noted that perhaps the aux fan works
    on stage 3(High Speed in both cases-Temp as well as pressure). The fans can be activated by either temperature
    or refrigerant pressure. According to MBenz data, here's the as-delivered
    Temperature and Refrigerant pressure vs stage activation:











    Auxiliary
    Fans Activation







    Switching Points




    1st




    2nd




    3rd







    Coolant Temp (ON in deg C)




    100




    107




    115







    Coolant Temp (OFF in deg C)




    95




    100




    107







    Refrig Pressure ON (bar)[psi]




    14 [206]




    17 [250]




    20 [294]







    Refrig Pressure OFF (bar)[psi]




    11 [161]




    14 [206]




    17 [250]







    Eq resistance of
    CTS (ohms)





    310




    250




    200







    Actuation of Fans (Volts)




    7




    9




    12







    It looks like the 2 aux fan is working on 3rd stage system!!!!



    3rd party reference(MBenz): The S500 series car has two (2) aux fans and are
    switched on in either two or three stages. Most of the newer Mercedes use just
    a two (2) stage system consisting of LOW and HIGH.

    Modification Kit: Available on 2 versions. (1) The original Cool Harness(CH)
    works for earlier Mercedes from 1987 to 1995.
    (2) Mercedes changed to this combo sensor starting with
    '95 model year cars. It combines the original CTS (B10/8) and ECT (B11/2)
    sensors into one housing. In the CH-V2, the ECT sensor is 'stock'. Also the
    modification to the CTS portion does NOT affect the ECT portion. Each
    sensor operates independently.

    Again where can we find/locate the related aux fan relays and so modification can be proceeded re-above?

    Please kindly provide expertise ASAP.

    Thank you.





  • virgo8bn Feb 03, 2010

    Dear lambertol_me(Expert),

    I see your point however the coolant temp sensor(CTS is good).

    For your info, the S500SEL sedan is from Europe(Europe version)
    ratherthan US and meant for tropical climate(Asia). The problem is the
    mechanic is having problem to trace where all these components were
    wired/connection and installed(eg Aux Fan relay; load resistors for the
    aux fan) for the various fan speed(assume a 2 stage, Low & High
    speed).

    Remark: some MBenz like series 190, the resistive components are
    mounted next to the engine however according to S500 databook the load
    resistor are upfront of the aux fan grille??

    Please clarify if possible

    Thank you.



  • virgo8bn Feb 03, 2010

    Thanks for the info charlymonty(expert),

    Fyi, the s500 Sedan is from Europe and not US. May have some difference
    in design and locations of components including wiring perhaps. Again
    this was meant for tropical countries(Asia) in particular. From other
    sources, it has always been a high temp issue(MBenz) due to
    inappropriate cooling design hence auto experts come to build
    modificatiuon kits. This modification is specifically
    for 1992-1995 'S' class cars such as the S500 or S600 (W140), coupes (C140) and
    500E/E500.
    Some
    models used the 2 coolant temp sensor(ECT(B11/2-with 4 male pins, for
    power train mgt and CTS-B10/8-for A/C & aux fan use, with 2 male
    pins and as recommended to install a 1.1kOhm resistor 1/4W across B10/8
    shall suffice) together with low load/high power resistors(R15 and
    R15/1 in series, 4W type?) installed. Otherwise recommended to use the
    so call the Cool Harness package(original CH or CH-V2) modification
    kit. Again assuming a aux fan relay is available for
    activation/switching since temperature sensor was installed(however for
    the 190E series, temperature switch is available)!

    Please help to revert soonest.

    Thank you.



  • virgo8bn Feb 03, 2010

    Dear charlymonty(expoert),

    Still cannot understand why the coolant temperature sensor(B10/8, after
    tested ambient to boiling water, resistance varies from 4kOhm to approx
    365 Ohm-100deg C) does not activate aux fan relay?

    Checked wiring connection of sensor as is not s/c!

    Remark: During engine running and a/con is switch on. When pulling out
    the connection to the B10/8(CTS), the aux fan run at high speed and
    connected back the aux fan stopped.

    Where can I locate the aux fan relay for the s500SEL(European model, export to tropical countries(Asia))?.

    Thank you.



  • virgo8bn Feb 03, 2010

    Dear fingaz22(expert),



    Fyi, the s500 Sedan is from Europe and not from US. May have some difference in
    design and locations of components including wiring perhaps. Again this was
    meant for tropical countries(Asia) in
    particular. From other sources in The US, it has always been a high temp
    issue(MBenz) due to inappropriate cooling system design hence auto experts overcome
    the problem by means of adding modification kits(“to fool” concept). This
    modification kit is specifically for 1992-1995 'S' class cars such as the S500
    or S600 (W140), coupes (C140) and
    500E/E500.

    Remark: For your understanding, when the B10/8 CTS connection disconnected, the aux fan run on high speed!




    From what I understand, it applicable to the 2 coolant temp
    sensors Mbenz Europe version where ECT(B11/2-with
    4 male pins, for power train mgt and CTS-B10/8(2 male pins)-for A/C & aux
    fan use. To DIY, install a 1.1kOhm resistor 1/4W across B10/8(two terminal connector).
    2 low value/high power resistors(R15 and R15/1 in series, 4W type, in US
    perhaps equivalent to the so called aux fan pre-resistor(R15)) to be installed
    in the aux fan circuit. Also one can buy the so call “Cool Harness”
    package(original CH or CH-V2 version available) modification kit. Again
    assuming a aux fan relay is available for activation/switching(however for the
    190E series, temperature switch(S25/1?) is installed instead of temp sensor)!. Unfortunately
    there is no adequate details of the modification kit used.



    Is there anyway to get the details of the modification kit technically
    and how to install/fix and kit/component sourcing?



    Will you be able to help on this(ASAP).

    Thank you






  • virgo8bn Feb 03, 2010

    High Termperature encountered as aux fans only run on high speed(engine coolant temp sensor set at 115deg C and 300# refrigerant pressure) on either cases!!!. Need to lower engine temperature by means of add ons if possible(say @90deg C, aux fan run at low speed during engine idling either with a/con on or off).
    History: A s500 Sedan MBenz(1992-1993 model, registered in 1994) from Europe and not from US this may have some difference in design and locations of components including wiring/circuitry perhaps. From other sources in The US, it has always been a high temp issue(MBenz) due to inappropriate cooling system design hence auto experts try to overcome the problem by means of adding modification kits(?to fool? concept). As recommended, this modification kit is specifically fit for 1992-1995 'S' class cars such as the S500 or S600 (W140), coupes (C140) and 500E/E500.
    Remark: For further info wrt the issue, when the B10/8 CTS connection disconnected, the aux fan run on high speed but plug in when the coolant temp about 100-110deg C(CTS resistance ~365 Ohm) aux fan still not running!
    (1) If you DIY, install a 1.1kOhm resistor 1/4W across B10/8(two terminal connector) with 2 low value/high power resistors(R15 and R15/1 in series, 4W type, in US perhaps equivalent to the so called aux fan pre-resistor(R15)) to be installed in the aux fan circuit. Will this works looking at the scenario mentioned???
    (2) In the market one can buy the so call ?Cool Harness? package(original CH or CH-V2 version available) modification kit.
    Again I would assumed a aux fan relay is still required.
    Unfortunately there is no adequate details of the modification kit nor the DIY circuit details available for conformance.
    Is there anyway to get the details of the modification kit technically and installation details wrt to install/fix the kit and components if any?
    Will any expert be able to help on this(ASAP).
    Thank you

  • virgo8bn Feb 05, 2010

    Dear Charlymonty(Expert),

    Thanks for the info, the briefs for the fan clutch is quite clear
    unfortunately there is more than what I would expect from the problem
    encountered. Mechanics said the engine radiator fan is working
    reasonably BUT ther following has been observed.:

    Firstly the aux fan ONLY works on refrigerant pressure at around 294-300# when A/C is on.

    Secondly whenever the engine temperature heated up to almost 115 aux fans sets in.

    In either case, the aux fan run at HIGH speed.

    I have compared with other S500 SEL owners and they said this
    version/model aux fan activation has been built to such specification
    and works on one speed. Perhaps be suitable for cold climate countries.

    Unfortunately in tropical climate countries, hot and humid it was a severe problem!

    Therefore I am seeking for any experts(practically experience) advice
    if they themselves have ever do such a modification(modification kit)
    to the temperature control circuitry so as to lower(fool the temp
    sensor) the activation point of the aux fans(say at/around 90deg C
    instead of 115deg C, the europe norms?) or by installing a robust add
    on kits.

    Thank you.



  • virgo8bn Feb 05, 2010

    Dear lambertol_me(Expert),

    The coolant temperature sensor has been checked and works
    fine(resistance vs temp) and the pressure sensor switch works ok s well.

    Its the single HIGH speed(@115deg C coolant temp or 294-300#
    refrigerant pressure switch) aux fan bothers me and surprisingly from
    history the car was made to run that way in the first place!. I try to
    look for modification kit(or DIY) either to enable the aux fans run on
    2 speeds(LOW &/or HIGH) or simple reason just run on single
    speed(HIGH) as per original design but with lower action point(say
    @90-95 deg C instead of 115deg C) for the aux fans

    Thank you.



  • virgo8bn Feb 05, 2010

    Dear Molson02536(Expert),

    Sorry if I have confused you.

    Both aux fans are working except both were kick in/activated by either
    115deg C coolant temp sensor or refrigerant pressure switch(294-300#;
    equiv to 20bar), the s500SEL originlly from Europe, model 1992-3 infact!.
    According to other auto experts, they hardly accept the car run on high
    temperature and this may weaken the engine performance in the long run. Their
    suggestion and to overcome it "DIY Kit or standard add on Kit" should
    be installed to the temperature control circuitry.

    The thing is I need to seek expertise advice if they themselves has any
    experience on such a kit installation perhaps to provide further details on how
    it was done and its performance; is the kit is readily available in the
    market???

    Thank you.


  • virgo8bn Feb 07, 2010

    Dear Sholly-NG(Expert),

    Thanks for the feedback and advice.

    It fact my car problem in the first place is:- It looks like the car
    aux fan only works on ONE speed(High) activated by coolant temperature
    sensor at high temperature(115deg C!!!) and originally design that way.
    But I need to know how can the aux fan be operating at a lower coolant
    temperature and perhaps run the aux fan at high speed and try to
    maintain the engine run at lower temperature(with the assumption of
    lowering the aux fan turn-on point would do the job!).

    What I would like to know if this is one way to resolve the high
    temperature problem which can be done by installing a modification kit
    to the original temperature control circuitry to "FOOL" the coolant
    temperature sensor!

    Remark: Any experts with experience on this are welcome. This is a S500 SEL from europe not from US!

    Thank you.



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8 Answers

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  • Master
  • 1,428 Answers

Really when cars have this kind of issues waht it relies on is the size of your radiator and the capacity of the fan.

It is a simple thing one can deal on by replacing the 1. Radiator to a higher capacity in volume of water; 2. the Thermostat and 3. the Fans as well.

That should settle the problem of heating at idle or at a stop.

Worry less. Thanks for using fixya.

Remember to rate this solution.

Posted on Feb 05, 2010

  • Titilayo Sodipe Feb 07, 2010

    Sincerely, there are ways you can go about this but forget the trial of getting the sensor deceived.

    Looking at the connector to the fan independently, you can run a wire to enable the two fans run simultaneously which will get the temperature of the car low and might even be very low depending on the capacity of your fans.

    Also, you might try a replacement on the Thermostat to that of a lower degree. Let's say 60-80 degree. I have used that once on a Mitsubishi Outlander and it worked pretty good.

    Good luck.


  • Titilayo Sodipe Feb 12, 2010

    Okay

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  • Mercedes-Benz Master
  • 3,854 Answers

From what you described, one fan only works and that's the second AUX fan. The primary fan does not come on is how i understand to what you described. Start with checking the high amp fuses and the relay to the radiator fan under the hood. Also check the wire harness and harness connection leads to the fan, look for and damages to corrosion or breaks. You can check to see if it's the ran it self that may need to be replaced by switching the wore harness from one fan to the other and see if the fan works or you can disconnect the wire leads from the harness and run a hot wire from the battery to the fan to see if the fan does work. If the fan does not work, replace the fan unit and if this is the case. Switch the wire harness from one fan to the other till you can get the replacement fan, this way the good fan will come on to cool the engine off before it get's to hot.

Good luck and hope it's a simple fuse, relay or a disconnected wire harness lead connector and not a bad fan.

Posted on Feb 03, 2010

  • Harvey N Tawatao
    Harvey N Tawatao Feb 03, 2010

    Here is a link for you and hope will help determine what is happening to your fan clutch system.http://www.k6jrf.com/MB_AAC.html

    Various actions of your cooling system (including the aux fans) under a variety of conditions are listed below:

    Thermostat will start opening at 85 to 89

    Thermostat will fully open at 102

    Viscous fan clutch will cut-in at 96 to 104

    Viscous fan safety cut-off will occur at engine rpm 4500

    The same will occur at fan rpm 3250

    Electronic fan (1st stage) will cut in at 16 bars of refrigerant pressure)

    Electronic fan (1st stage) will cut out at 11 bars

    Electronic fan (2nd stage) will cut-in at 107

    Electronic fan (2nd stage) will cut-out at 100

    A/C will go into 50%on, 50%off cycle (20 seconds interval) at coolant temp 121 to 123

    A/C will go into emergency shut-off mode at 126 to 128

    Pressure cap will open at bar 1.3 to 1.5

    Coolant temp max is 130

    Jump two white leads shown and you will have constantly running aux. fan (as long as ignition is on). You have to jump green and blue wires coming from the temp. sensor. The
    leads are female and each hooks up to a leg of a fuse. This way they
    are connected through fuse. Now with jumping the wires the Aux fan (Blue X Brown) Take a paper clip and bent it cut the small part and inserted it into both females runs not while the key switch is
    on the "On' position, it will run only when the engine is running. I
    think the temp sensor is the one working on the 'ON' position that is
    why. The fuse you have put is really of no use (I think) because I checked
    the fuse box on the driver side where all the fuses are located and I
    found out that when removing the fuse (far one to the right ... The one
    isolated with a C mark) the Aux fan will stop. So I think with the new
    setup it is fused too.

    Good luck and try this for now till you can find out if your Clutch fan has gone bad, this will keep your engine running not to hot.



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Check your coolant temp sensor this shld give a signal to the ECU that the cooling fans shld work. The sensor for the ac discharge pressure is different form the coolant sensor.

Posted on Feb 02, 2010

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  • Mercedes-Benz Master
  • 17,970 Answers

Here you have several item for check it:
1 Inspect > Hose > Ruptured, Cracked or Leaking Raditor Hose.
2 Inspect > Head Gasket > Leaking Head Gasket.
3 Inspect > Thermostat > Thermostat Stuck Closed.
4 Inspect > Raditor Cap > Worn or Damaged Raditor Cap.
5 Inspect > Raditor > Raditor Fins Obstructed.
6 Inspect > Belt > Missing or Broken Water Pump Belt.
7 Inspect > Heater Core > Heater Core May Be Leaking Antifreeze/Coolant into The Vehicles Floor Area.
8 Inspect > Intake Manifold Gasket > Leaking, Worn, or Damaged Intake Manifold Gasket.
9 Inspect > Relay - Raditor Cooling Fan Motor > Faulty Cooling Fan Relay.
10 Inspect > Fan Blade > Broken, Missing, or Faulty Fan Blade(s).
11 Inspect > Cooling Fan Switch - Raditor > Faulty Raditor Cooling Fan Sensor/Switch.
12 Inspect > Water Pump > Leaking Water Pump.
13 Inspect > Raditor Fan Motor > Faulty Raditor Cooling Fan Motor.

Hope this helped.

Posted on Feb 01, 2010

  • 1 more comment 
  • ZJ Limited
    ZJ Limited Feb 02, 2010

    Initially, I can overtake these interesting references...
    -http://www.k6jrf.com/MB_S500.html ( check item 18 f
    or the problem of high temperature )

    Other,
    sometimes a water pump will fail internally due to severe corrosion
    wearing away the impeller blades, or the impeller comes loose on the
    shaft, or the shaft itself may break from metal fatigue (caused by
    flexing due to an out-of-balance fan).

    The pump may not leak,
    but it may not circulate enough coolant through the engine to keep the
    engine at normal operating tempera


    One way to test for a bad water pump is to squeeze the upper radiator
    hose when the engine is hot and idling. Careful, because teh hose willb
    e HOT! If you do not feel much coolant circulating through the hose
    when you rev the engine, the pump may be bad.

    See u soon for more (if I find)


  • ZJ Limited
    ZJ Limited Feb 02, 2010
  • ZJ Limited
    ZJ Limited Feb 02, 2010

    This relay is under a black plastic cover on the left side of the engine bay.

    Check here for the FSM Wiring Diagrams, and here for other graphics refereneces: autorepair faqs

    Good luck.

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You will have to check out the fan clutch.Fan Clutch test
First, lets discuss what the fan clutch does and why it is there. The fan clutch is just what the name says, it is a mechanism that will clutch the fan on and off depending on the need for more or less cooling air to flow thru the radiator. It is a thermostatically controlled device that when operating normally will vary the fan speed independently of the engine speed. When cruising down the road at freeway speeds, with outside temperature less then desert conditions, the fan should be merely be idling along, turning just fast enough to add a little air flow when needed, in
this way the fan noise and drag on the engine is greatly reduced. When reducing speed, the fan clutch will sense higher temperatures thru the radiator and “clutch up” thereby increasing the fan speed to help maintain constant engine temperature. It may in fact, cycle as the temperature of the air thru the radiator changes depending on airflow. If the fan clutch operation is normal, when first starting the car , the fan clutch should “clutch up” and an increase in noise and airflow should be obvious. After about 60-90 seconds, the fan will un-clutch and the noise and airflow will drop. The fan will continue to turn but at a much reduced speed. As the engine warms and
the thermostat opens to regulate the temperature, the air thru the radiator gets hotter and the clutch will sense this, thereby increasing the speed of the fan to maintain a normal operating temperature.

First signs of trouble:
A normal temperature indication at freeway speeds and an increasing temperature as the vehicle slows is one of the first indications of trouble. Many other things may give this indication but if the temperature seems to be stable at speeds but climbs in traffic or while stopped, this is a good indication that the fan clutch isn’t working correctly. As the temperature continues to climb, the auxiliary electric should start but may not provide enough air to keep the engine from overheating.
Another sign of trouble is if the fan noise is high and never decreases after starting, and is there anytime the engine RPM is higher then idle, this means that the fan clutch is “frozen” and is not releasing. Although this will not result in immediately serious trouble, it will load the engine continually and gas MPG will be reduced. Load on the fan belt(s) will be higher and shorten the life of that component also.------

The externally mounted resistor near the coil is the distributor resistor.
it appears that the ballast resistor terminal is located within the housing (casing) of the starter solenoid .
This will help. Thanks please keep updated.please do rate the solution positively .thank you for using fixya



Posted on Feb 01, 2010

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I don't have the diagrams i can send to you. but the relay is the most common issue for this problem seeing what you have stated. very good by the way with all the details it really helps us give a more educated answer to the problem.

Posted on Feb 02, 2010

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2 possible culrpit

fan switch connected to the ...

water temp switch connected to the...

water temp sensor.... so make that three.

you would need to get a service manual to help you out in removing the parts for testing, repair and replacement because i would need to illustrate it and would take days if i do,

here is the manual

http://www.pdfee.com/mercedes-benz-operators-manual-ml-320-se-420-sel-500-sel-pdf.html

Posted on Feb 01, 2010

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This would be due to your fan clutch. replace your fan clutch. they run about $125 and will end your overheat issue. dont let these things get about 90c. you will warp the heads and end up replacing your head gaskets. the very fact that the fans come on is outstanding. cheers

Posted on Feb 01, 2010

  • 2 more comments 
  • Kori Policy
    Kori Policy Feb 01, 2010

    when the a/c is on it will turn on the fans low speed until it reaches a higher temp. when it reaches a higher temp, it will turn it on high, but you still need the fan clutch. this is what keeps the cooling system at a steady temp until the fans kick on. these are filled with a viscous fluid that as it heats up flows through the veins and allows for stronger air pull through the core of the radiator, thus cooling the system.

  • Kori Policy
    Kori Policy Feb 01, 2010

    i guess i havent been clear, the fan clutch is a mechanical unit that is bolted to the front of the motor. no electrical components to fool with. if you open your hood and look at your fan attatched to the engine, you will see a silver, veined unit in the centre of the fan. this is your failing unit.

  • Kori Policy
    Kori Policy Feb 01, 2010

    there will be a inverted hex bolt in the centre going to the pulley(this is your mounting point) and once off you will see the 4 bolts that hold the fan to the fan clutch.

  • Kori Policy
    Kori Policy Feb 01, 2010

    On the aux fan side, I have been there and can add some comments. When you pulled the temp sensor from the engine, the fans should go to high speed. This is a fail-safe mechanism in case a temp sensor wire gets broken or loose. This indicates the high speed fan circuit is ok. The fans should come on at low speed at any temp when you initially turn on the A/C. (they may cycle on and off as well). If that is not happening you probably have a break in the low speed circuit, probably either a relay or a resistor problem

    Note: in 95 mercedes instituted a running change on the fan resistor assembly. They made it a 2 speed operation (low/high) and replaced the ceramic resistor assembly with a single low speed encapsulated resistor. It appears as a verticle rod approx 3/8 in diameter and 4 inches long sitting front of the AC condensor/radiator. This was a mistake by Mercedes since the resistor (rod) burns out prematurely. The affects low speed operation. The Mercedes parts instructions call for the unit to be replaced by the old ceramic resistor assembly. You can do the checks with a simple VOM.

    If the resistor wiring is ok and the relay checks out, you likely have a defective climate control. Changing the value of the resistor values to fool the climate control seems like a workable solution. It may shift over time, however. Also, don't trust the temp guage. Always calibrate coolant temperature with a digiital thermometer

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