draco

It seems that the last place that did my servicing (it was Toyota), did a fine job but it always seem as though they service the car with out the air-con in mind. I have had this happen on my previous cars as well. When the car is idling (i.e. not in drive) it is nice and smooth, no hint of any "vibration" but when the A/C kicks in the idle drops the revs and obviously the car adjusts to keep at normal idle level. While the A/C has kicked in, there is a slight vibration that you feel in the car, through the seat. When it kicks off it goes away. Do mechanics not do the servicing with the A/C on so they can get the idle smooth at this point rather than set the idle when A/C is not on? Nothing wrong with the A/C, belts or anything, it's just that I have experienced this in many a car.

kiwi

as per service manuals, the idle is set with nothing on, no A/C, no headlights, no radio, nothing, its just how its done.

veleno

iTrader: (3)

Sounds like every car I've been in. I think this is normal considering the engine has to accommodate for the extra "stress" of the a/c when it's turned on.

mowmow

X2, that is exactly what I thought too.

SChema

iTrader: (2)

It's just the parasitic load placed on the motor like power steering, alternator and the water pump. Those are always going to be used, unlike the AC compressor. Idle is set to spec with all the necessary loads. If it was set with the AC running, the idle would rise when the AC is off.

Hayk

iTrader: (1)

Not true. It would drop because there would no longer be any load on the engine. It's just it would be inaccurate if you set it with the AC on.

kiwi

That and your definition of parasitic load is incorrect, parasitic load is the power used by the car when everything is turned off.