Audi C4 AC Control Unit Coding

Hello, first of all, a huge compliment to this forum. Even as an amateur, you can really learn a lot here... Respect!!
I have been a loyal Audi A6 Avant driver for 5 years (model year 12/96, AAT). Now, with 225,000 kilometers on the odometer, the problems are slowly starting to accumulate. I initially wanted to buy the next-generation model, but in the end, it's a gamble .
Regarding the engine, I'm very satisfied with my R5. It has extremely low oil consumption (0.2 - 0.3 liters every 15,000 km), so I decided to replace the timing belt, have the fuel injection pump adjusted, and replace all the glow plugs. Now it runs like a kitten again. I'm also going to reactivate the factory-installed auxiliary heater, a Webasto DBW46, and then winter will be much easier to deal with.
Now, regarding my big problem... I haven't found anything in the forum, despite an extensive search .
My air conditioning system isn't working anymore; it's showing a belt slippage error (according to VAG). It's almost certainly the control unit. So, given the weather, I figured there must be good deals on eBay, and I bought a climate control unit that was supposedly in perfect working order, but with a defective display. I replaced the display and took it to VAG for coding (it was from a B4 040). Despite multiple attempts (00053), I always got the message that none of the actuators were receiving power. The technician said that a C4 has more components in the air conditioning system than a B4 (an additional flap?), and that it probably wouldn't work.
The engine control unit is from a 1992 vehicle; could that be the problem, or is it actually not possible? If this topic has already been discussed many times, please forgive me...

Christian from Minden.

Part numbers? Used part/new part?

Hello,
The part number of the defective old device is 4A0 820 043 K.
The part number of the purchased Audi B4 climate control unit is 8A0 820 043 E.
I also bought a new device cheaply for A3/A4, which I will try again at VAG-H on Thursday.
The part number is 8L0 820 043 E.
Is it generally possible to reprogram any Hella devices of the same type, perhaps the first device is also defective?

Greetings from OWL.
Christian.

How do you conclude that the parts are identical? In my opinion, what you're trying to do doesn't make sense. You either need another 4A0 820 043 K or a 4A0 820 043 M.

Well, I once read something in another forum. The guy who sold me the first climate control unit assured me that it would work, claiming he had already installed one in an Audi Coupe (C4 model) and that it worked, and that he works at VAG... yeah, right, sure.
I'll probably have to do some more searching and sell my acquired equipment again when the temperatures are warmer. And should I give up on a device with the number 4A0 820 043 H, or is there still hope? I think used devices from K year 1996 are very rare...