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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From 300CE to SLK230K

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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MERCEDES Benz Master Guild Technician (6 TIMES)
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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)
Retired Moderator

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?

__________________
From 300CE to SLK230K

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.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

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).

__________________
From 300CE to SLK230K