Taking a look at the schematics there are two actuator controls, one each
for the driver and passenger that control the temperture. The actuators are
on either side of the HVAC module case (the air plenum inside the car).
Both actuators are controlled by the HVAC Control Assembly which is the
module that has the HVAC controls. The actuators and control module share
the same fuse, so it's not likely that their is a power issue. The shop
manual also says that a code should be set if problems with the HVAC control
assembly are detected. Do you have any codes? To read the codes on a C5 do
1) turn on the ignition but don't start the engine.
2) press the "reset" button to turn off any warning messages
3) press and hold "options" and
4) while holding "options", press "fuel" four times within a 10-second
The shop manual does describe a process where the HVAC control can
"re-calibrate" the actuators (usually after one of them has been replaced)
which is done by pulling the HVAC fuse (#27) and putting it back. It says
this process takes about 60 seconds and each actuator is moved from fully
open to fully closed to calibrate them. If this doesn't fix the problem you
could have a loose connection on the HVAC control module, or the control
module is bad.
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