06 Azera Limited -- Different Air Temps Between Dvr/Psgr Ducts

2006 Hyundai Azera Limited
130k miles

The car features a dual-zone climate control system. With AC on, the air temp from the driver-side ducts is noticeably warmer (not hot) than the passenger-side ducts. P-side works perfectly. This is a common phenomenon among many makes/models, and the t-shooting process is identical among all: check the damper actuators and/or motors.

After I removed the "driver's temperature control actuator" (p/n: 97159-3K000) I flipped the air mix damper manually back/forth and checked the air temperature at the duct with engine running. Air temperature changed between hot and warm. I also changed the temp on the control panel and watched the actuator motor move. I presume from these tests that both the d-side actuator motor and air mix damper work normally, and the control systems work as they should.

And that's pretty much the extent of my t-shooting prowess with this specific problem. I'm officially stumped.

What else should I look at?