After re-reading Mark D's comment 3 times I finally understand what he was
saying
about the rpms remaining the same.   I agree that the engine speed does
increase
slightly but not to the point of seeing an rpm increase on the tach.   I've
never seen
that with turning on the AC other than a momentary bump.   So if you are
seeing an
100 - 200 or more increase in the tach speed for AC only there is
definitely an adjustment
that is off.   My idle has always been under any condition 1K RPM.   And
only has varied
from that with a faulty O2 sensor.  There must be a signal from the AC
control panel that signals the ECU for this operational change.   I would
check there first.

Steven
91 Westy

On Fri, Oct 17, 2014 at 10:34 AM, mark drillock <mdrillock@cox.net> wrote:

> 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
>>
>>