My 2006 2500 Silverado dual auto climate control always blows on high in auto. I can manually control the fan speed but in auto only blows on high. Temperature setting makes no difference. All the blend doors seem to work as they should.

 

You need to see how to adjust the fan speed setting while the HVAC is in Auto mode, and then set the fan speed to your desired speed and save it. This should be spelled out in the owners manual. If you do not have an owners manual, google will be your friend.

Good Luck!

 

In auto mode, the control module has full control over the fan speed. It will blow on high until the cabin temp sensor detects the desired temperature is reached, then it will vary fan output to maintain the temperature

The size of the cab will be the primary factor in how long the fan blows on high (secondary factors being the cabin temp at startup and the ambient temp), but typically it doesn’t take longer than 5 minutes.

If you’re concerned there’s an issue with the cabin temp sensor, a scanner capable of reading body codes and displaying live data will be the most efficient way to diagnose it.

The temp sensor is located above the driver seat, between the A and B pillars, under the headliner. Removal of the sunshade and A pillar trim will be necessary to access it.