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1999 SL500 heat problem

Discussion in 'General Mercedes-Benz Related Discussion' started by macdoesit, Sep 12, 2017.

  1. macdoesit

    macdoesit Active Member

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    My heat gage normally reads 80, noticed today when idling it goes to 90. I went to raise hood and the hood was so hot could not lay the palm of my hand on it. The fan was turning but the 2 electric fans were not turning.
    Anyone know what the problem might be and how to fix.
    Thank you
     
  2. mikestrivens

    mikestrivens Senior Member

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    the two fans are for the aircon and only come on to cool the refrigerant. Temp gauge seems to be fine so I'd say there is no problem. What was the air temp? Has the hood lining broken down? I had to replace that on both my cars recently.
     
  3. LostKiwi

    LostKiwi Senior Member

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    As Mike.
    The two electric fans are for aircon or (this may be year dependant) if engine temp exceeds 95 degrees C. At the temp they will come on low speed then if temp exceeds 105 (from memory) they will switch to high. This is certainly true for 129s from 93 to 95.
    Sounds to me like you've had a hot day and air temps rose so the cooling system is unable to lose heat as easily.
     
  4. OP
    macdoesit

    macdoesit Active Member

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    Thank you.
    The ambient temp was a cool 75* and the hood insulation is rotted falling off.
    Where can I get replacement hood insulation ?

    Another question. When ac is on why is there no condensation dripping from under car ?
     
    Last edited: Sep 13, 2017
  5. LostKiwi

    LostKiwi Senior Member

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    Fans weren't turning? Suggests aircon was off. Which will also explain why no water was dripping under car.
     
  6. OP
    macdoesit

    macdoesit Active Member

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    I first noticed this Summer when ambient temp 95* and ac on high and no condensation dripping.
     
  7. OP
    macdoesit

    macdoesit Active Member

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    The hood will burn your hand, that has never got that hot before. The temp gage has never been above the 80 mark.
    Thank you for replies.

    Where can I buy replacement hood insulation ?
     
    Last edited: Sep 13, 2017
  8. mikestrivens

    mikestrivens Senior Member

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    Hood insulation can be purchased from Mercedes.
     
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  9. OP
    macdoesit

    macdoesit Active Member

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    Thanks mikestrivens.
     
  10. mikestrivens

    mikestrivens Senior Member

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    It is a horrible job to replace so I'd get Mercedes to do it.
     
  11. OP
    macdoesit

    macdoesit Active Member

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    Thanks
     
  12. OP
    macdoesit

    macdoesit Active Member

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    I let the car idle in my shop, when gage went up to 100 C the 2 fans came on and went off at 90 C and continued to cycle in those heat ranges And the ( AC ) was not on so that tells me those electric fans are for motor, radiator heat.
     
  13. LostKiwi

    LostKiwi Senior Member

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    Like I said earlier.....

    The two electric fans are for aircon or (this may be year dependant) if engine temp exceeds 95 degrees C. At the temp they will come on low speed then if temp exceeds 105 (from memory) they will switch to high.

    To expand on that:
    The electric fans on the are triggered by AC refrigerant pressure for the low speed fan.
    If the engine temperature sensors detect an engine overheat (in excess of around 95 degrees) the fans will kick in irrespective of AC setting. If the temperature then continues to rise the high speed setting will take effect at around 105 degrees (from memory) until the temperature falls.

    What you are seeing is therefore completely normal but I question why your fans are not kicking in for the aircon.
    That suggests a fault in the aircon side as those fans are required to cool the refrigerant.
    When you turn on the aircon the compressor raises the pressure on the high side of the circuit. This is where the aircon pressure sensor is hence the system turns on the fans once the compressor is running. There is a second aircon pressure sensor that will tell the aircon compressor to engage or not - the compressor won't engage is there is no base pressure in the system (for example as a result of a leak).
     
  14. OP
    macdoesit

    macdoesit Active Member

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    Are you saying that when the ac is on the low speed fan will stay on as long as ac is on ?
    I still don't understand why there is no condensation dripping on the ground when ac is on.
     
  15. LostKiwi

    LostKiwi Senior Member

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    That's exactly what I'm saying. Air con is a heat pump. One side gets hot in order to make the other side cold. That heat has to be removed. That's why the fans run.
    With engine running and aircon on you should see the aircon compressor spinning. There are three rivets on the front of the compressor. They should be spinning.
     
  16. mikestrivens

    mikestrivens Senior Member

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    Easy to check if aircon is working. Does it get cold in the car?
     
  17. OP
    macdoesit

    macdoesit Active Member

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    I have owned the car 5 years. The ac on the Benz will freeze you out so why does it not drip water on the ground ?
    I have 5 other vehicles and they all have one fan that takes care of rad and ac so finding out that the Benz has its own condenser fans is new to me.
    The other 5 vehicles will leave a puddle of water on the ground when ac is on but the Benz does not.
     
  18. mikestrivens

    mikestrivens Senior Member

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    Stop worrying it is all fine.
     
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  19. LostKiwi

    LostKiwi Senior Member

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    Check for wet carpets around the footwell - the drain pipe may have fallen off and be draining into the cabin.
    If thats all dry and the aircon works then there's no problem.
     
  20. OP
    macdoesit

    macdoesit Active Member

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    Ordered the hood insulation and spray adhesive will pickup Friday. Thanks
     
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