W124 airco, ventilation and electrical mess

[Mergola]

Hello there.
I bought w124 300E sedan petrol 1986 (euro) recently and inherited an electrical mess that I'm trying to sort out for couple of weeks now and at this point I'm getting frustrated.
First off, I'm getting hot air all the time regardless of what I switch on or off so that's what I started with.
I checked many forums, bought the service manual, multimeter and started with the duo valve.
Found one on the cheap , tested it and it works, in fact the old one worked too it just wasn't geting any voltage to it.
I tested pins on the climate unit connector with ignition on and was getting 4.5V on one side, and 5.4 on tghe other, that doesn't seems right to me because the duo valve needs 12V to close the hot water.
I powered the duo valve from battery and it does close, that's how I'm driving atm until I figure this out.

Next, climate control panel.
I have 3 of them so I'm guessing at least one of them should work right?

I found the little blower inside the glove box and it works, it does suck air from the roof hose that is attached to the cabin air sensor and here I encountered the first problem.
I don't know how to test that little sensor so I'm trying to buy one or two of those just in case, but I can't seems to find it anywhere in europe.
If I knew the mercedes part number of it I could look for it that way I guess.
In meantime, is there a way to test the sensor if it works?

Also, I found this part behind the glovebox:
Bosch 'Temperaturregler' (temperature regulator) 1 147 328 043, merc number 000 022 1503
I have the wiring diagram of my car but I can't find this part in it or anything AC system related for that matter :/
Can someone explain to me what's the job of this part and how to test it with multimeter please?

Further, are there any other sensors and thermostats that could be related to this issue that I could test/replace?

I'm a total novice when it comes to wirings and anything electrical so I really need some help here because if I bring the car to Merc dealer they will skin me alive, probably charge me more then I payed for the car heh, so I'm trying to at least troubleshoot the problem myself and anything else I can do to dodge a massive bill.
Thank you for reading.

 

[mattkh]

Which country are you in, a cold climate or a hot one..?
I do not have a wiring diagram for your car.
Please put up a picture of the climate control panel on your car.
Also a picture of the connector to this unit, but make sure the colours of the wires are showing correctly.

 

[Mergola]

I live in The Netherlands, cold climate and always rainy.
Wiring diagram from the owners workshop manual:


The panel: (found the pic on google so it's not mine but it's identical)


I'll take a picture of the connector of the temp regulator later today.

 

[Mergola]

Which country are you in, a cold climate or a hot one..?
I do not have a wiring diagram for your car.
Please put up a picture of the climate control panel on your car.
Also a picture of the connector to this unit, but make sure the colours of the wires are showing correctly.

More info and pictures
The heater system:

My control panel:
:
Connectors of the temperature regulator thingy:


I haven't even started on the actual electrical mess which is the AC system.
This is what I have to deal with:

The cabel for what I assume is the AC system is cut off and only the black wire is used which goes to the AC compressor I'm guessing, then someone instaled switches for the compressor and the additional AC fan or whatever it is, under the steering wheel:

One switch turns the compressor on and the other the fan but it doesn't blow any cold air so I stay out of it for now, I did refilled AC gas though, it's when I found out about this AC issue.

Obviously some rewiring is needed and I plan to bring the car to a electrician expert but before I do I'm trying to make sure that all sensors, relays and control panel works so I don't have to leave my car there for too long, wait on hard to find parts orders etc.
Besides, the constant heat blowing inside shouldn't be there even without the AC system so if I can at least fix that, as in, when control panel wheel is set on max cold to send 12V to the duo valve so it closes the hot water circulating to the cockpit, I'd be satisfied and worry about the AC rewiring later.

 

[mattkh]

Thank you so much for the photos.
I need to do some research now about your car.
One thing though, cleaning and checking all the earth connections you can see and reach may be an idea.

 

[mattkh]

I don't know how to test that little sensor

This little sensor, you can check its resistance with a multimeter. Then blow some warm air onto it and see if the resistance changes.

 

[Mergola]

I don't know how to test that little sensor

This little sensor, you can check its resistance with a multimeter. Then blow some warm air onto it and see if the resistance changes.

I checked voltage around the sensor, while ignition on, the connector gets around 7V, then directly on the sensor wires, I get 3V.
When not powered, zero resistance, zero ohms.
Blew hot air with blowdrier, same deal.
I just want to replace it but can't find it anywhere, so I went to electronics shop to try and buy the little blue sensor and connect it to the housing.
The dude in the shop obviously didn't have it but he tested the ohms too and said no resistance is good on such little sensor and told me those sensors never really go bad and that mine is working so I don't know what to do with it, reinstaled it to my car and that's that for now.

He also sold me some diagnostic chip that you plug into the diagnostic plug (X11 on the diagram) and via bluetooth and software it gives you codes on your laptop etc.
I don't know if it works or if it's a gimmick of some kind but that's what I'll be doing tomorrow hehe.