Re: Sluggish AC on a 164 digest V7 #733

[C M Smith <cmsmith@domain.elided>]

The automatic climate control on the 164 is truly hopeless. The only time
it really works is on the highway and then only if the ambient temp is not
too different from the interior. One problem is the dumb location for the
interior temp sensor which is the key to the feedback loop to the computer
adjusting the cabin temperature. In the 91 164 this sensor is in the roof
"console" behind one of the funny little vents, the other is just a dummy
vent to make the console look symmetrical. A tiny fan draws cabin air over
the temp sensor which then signals the temp controller to warm up or cool
down. Trouble is, the sensor only measures the temp at the roof! SAAB uses
a much better system where the analogous component is behind the dash right
smack in the center of the dash and behind the fascia. This then measures
the average cabin temperature.

When the sensor fails it's usually the fan, which then causes the cabin
temp to vary all over the place. If your AC blows cooler when you reduce
the selected temperature, I'd suspect the sensor. If reducing the set temp
makes little difference, I'd suspect your AC unit is needing a recharge, or
the compressor needs a rebuild, or perhaps the drive belt is slack,
although due to a particularly dumb design, a slack ac drive belt also
means your alternator is not getting full drive because it's driven off the
ac pulley!

I assume you know about the stepper motor problem which could also cause
the symptoms you describe. As the stepper gearbox on the temp control loses
a few teeth the climate control will no longer be able to accurately and
quickly respond to the different airflow resulting from different vehicle
speeds, and your interior temps will go wacky.
Michael Smith
Calgary, Alberta
Canada
91 Alfa 164L, White, original owner 

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