The idle is supposed to increase when the A/C is on. There is a wire
from the A/C compressor clutch over to the idle control unit so the idle
control unit will know to increase the idle speed so the A/C doesn't
stall the engine. I don't know what the idle speed rpm increase is
supposed to be but maybe someone else does.

That year should have the later trinary pressure switch and this could
be giving a false indication of a need for medium fan speed. Or maybe
someone could have fooled with the wiring to make it do this?

Mark

Dan N wrote:
> hi all,
>
> 1990' Carat - recently purchased - rebuilt engine - smooth idle 950 RPM -
> A/C recently serviced, cold air, new fan switch.
>
> When I turn the A/C on the idle jumps to 2000 RPM - the fan goes to medium
> speed all the time.
>
> What part or parts that triggers the idle?
>
> What part or parts that triggers the fan?
>
> please help -  I search in the archive and only found an April 2000 article
> about this..
>
> many thanks in advance
>
> dan
>