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StephFR 08-12-2006 04:46 PM

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?

mbdoc 08-14-2006 08:35 AM

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.

StephFR 08-14-2006 06:37 PM

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?

mbdoc 08-15-2006 08:12 AM

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.

StephFR 08-15-2006 12:18 PM

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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