GM Service Manual Online
For 1990-2009 cars only

The buttons for the heated and cooled seats are located on the climate control system.

(Heated/Cooled Seat): Press this button to turn the feature on. The button on the left controls the driver's seat and the button on the right controls the passenger's seat. Each press of the button will take you to a different setting. The settings available in order are HI HEAT, LO HEAT, OFF, HI COOL, LO COOL and OFF. You will be able to feel the temperature change in a few minutes.

The feature will automatically turn off when the vehicle is turned off.