The center dial on my S70's climate control unit doesn't do anything... no dampers change to adjust air flow. The other two dials do work, and the fan adjusts its speed to match the thermostat setting selected. I had the dash out twice -- once to fix the broken dash mount brackets and again recently to perform an A/C evaporator replacement.

Any ideas on how to debug this? I'm assuming that when you adjust that dial, it's not a mechanical linkage--a step motor somewhere is adjusting something that maybe I didn't get reconnected correctly? Fortunately, the air is blowing out the main dash vents, so the A/C is working fine (cooling ME), but this could be a problem come winter if I can't get heat to the windshield.

 

That an ECC (electronic climate control); does it flash any codes when you pwr it up? If so, read them; that's where I would start.

 

I'm having similar issues with my ECC but I have a 96 850 with the automatic climate control. (there is no diagnostic unit under the hood). I've replaced the resistor and the main ECC, but used salvage parts. Yes, I know the salvage parts could be nonfunctioning as well. The unit works occasionally, but cold weather is coming and that defroster is important. An ideas on how to troubleshoot the system?

Did someone say I can buy a manual ECC and plug that in instead?

 

There is a part in the dash that is often broken. It's a linkage arm that is white/plastic. It connects to the bleed motor, the motor will work, the arm is broken and will not adjust the flap in there to re-direct the air flow. I have a video of it, let me try to find it. It is located behind the glove box in just to the drivers side of the fan, in a crevice.

It wont throw a code because everything electrical is working.

 

Circled in yellow.