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  #1  
Old 08-12-2006, 04:46 PM
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A/C ON: RPM supposed to be higher and aux fan to kick-in?

My car is less responsive at lower RPM (under 2500 rpm), tipically when starting from stop, only when the A/C is ON.

I understand that the compressor add a load to the engine, but it's really noticeable, like the car having difficulty to get higher RPM up to 2500.

I noticed something strange:

- when I turn A/C on at idle, the engine is not increasing RPM (I thought it was the case on any car to compensate for the load...),

- the auxiliary fan is not engaging: again I thought it should cycle to help A/C efficiency (cooling better its radiator). Car get hotter faster, probably due to that.

Something wrong?
What component is supposed to control higher RPM and fan auxiliary when A/C is ON?

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Last edited by StephFR; 08-14-2006 at 06:38 PM.
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  #2  
Old 08-14-2006, 08:35 AM
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The RPM shouldn't increase but remain the same as with the a/c off.

The CIS control unit controls the idle circuit.


The aux fan should come on when the engine reaches 107C or when the a/c system pressure reaches 16bar...about 240psi on the high side.
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  #3  
Old 08-14-2006, 06:37 PM
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Thanks for the information.

Are those values for the first speed of the aux fan or the second? If this for the 1st: when the 2nd speed get in?

What can cause the car to be slow geting RPM up to 2500 when A/C is ON?
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Last edited by StephFR; 08-14-2006 at 07:37 PM.
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  #4  
Old 08-15-2006, 08:12 AM
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That CIS-E M104 engine makes very little torque at low RPM & with the A/C compressor engaged & blower on the engine is OVERLOADED until the revs are higher

Aux fan high speed only with engine temp, approx 107C &
low speed only with A/C pressure above 16 bar.
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Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
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  #5  
Old 08-15-2006, 12:18 PM
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Thanks for the info.

I was expecting low torque at low RPM from a 24 V engine, but not such difference. If A/C is taking like 5+ HP, make sense (is it? just for my knowledge).

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