AC blower issue
 

I have a 96 s320 with an ac issue. If the blower is on high or low it works fine. If you select auto it runs on high for a few seconds then switches to the low fan setting even though the display still shows the high setting. even if you manually increase the fan speed it stays on low. Is this a bad ac control unit?

No it is the blower motor regulator, common failure point on that car. You can sometimes source the regulator without the motor.

Had the same issue with our 98 S500