Dual heat not working properly

Hi,

It sounds like the blend door actuator for the left side has failed. What I would recommend is to remove it and see if it responds when you actuate it to work.

Here is a link that shows in general how one is replaced:

https://www.2carpros.com/articles/replace-blend-door-motor

Here are the directions specific to your vehicle for replacement. the attached pics correlate with the directions.

______________________________________
2005 Cadillac STS V8-4.6L VIN A
Air Temperature Actuator - Left
Vehicle Heating and Air Conditioning Air Door Actuator / Motor Service and Repair Procedures Air Temperature Actuator - Left
AIR TEMPERATURE ACTUATOR - LEFT
AIR TEMPERATURE ACTUATOR REPLACEMENT - LEFT

REMOVAL PROCEDURE
1. Remove the left closeout panel.

pic 1

2. Disconnect the left air temperature actuator electrical connector from the actuator.
3. Remove the left air temperature actuator screws.

pic 2

4. Remove the left air temperature actuator.

INSTALLATION PROCEDURE

pic 3

1. Install the left air temperature actuator.
2. Install the left air temperature actuator screws.

NOTE: Refer to Fastener Notice in Service Precautions.

Tighten the screws to 1 N.m (9 lb in).

pic 4

3. Connect the left air temperature actuator electrical connector to the actuator.
4. Install the left closeout panel.

________________________________

Let me know if this helps or if you have other questions.

Take care,

Joe