Even when the car is cold, the air temp is not, so I'm inclined to think it's not the duo valve.
Is it possible that the ambient temp on the gauge cluster not reading could have something to do with it? It's stuck at -38 or something like that. One of the threads in that search mentioned by @jbanks15
said something about it possibly causing problems with the a/c as well as the fuel mileage.
From my own experience(s) ..
When I had a broken external air temperature sensor on my (admittedly non-A/C) 200 - see thread HERE
- it made not one jot of difference to the heating system and I ran it without that sensor for a couple of years or more. The only thing that that sensor appeared to do was to tell me what temperature the external air temp was at.
I had non-working duos on my 320 so I've been there as well ..
You fail to say how non-cold your cabin air actually is, can you define that? i.e. Ambient, Warm, Hot?
If the A/C is not working and the duos are
, you will still get ambient air temp at the vents - just like switching the A/C off
If the A/C is working but the duos are not
, you will get air IRO 48°C
During my small quest to sort my own duos out, I did manage to ascertain that there's 4-5 possible causes for non-working duos:
1. Duos are kaput
2. Broken wire to duos
3. Fuse 15 is blown
4. HVAC Controller is FUBAR
5. Faulty Internal Air Temp Sensor