I tried the heater control unit from a B7 model and noticed the wiring difference, my cabin air temp won't stay at a steady warm temp. From a cold start this is what happens.... Heater set at 22c in a few minutes of driving I get warm air when the engine temp is indicating roughly 50c the heater starts blowing cooler air (this is intermittent but 80% of the time) put the heater to 24 and it'll blow warm for a while then cool down, increase to 26 same thing happens, I've had the heater at 28c and still blowing cool air, at this stage it'll only blow warm on HI. The other 20% of the time it'll maintain a steady flow of warm air.
On trying the B7 unit it maintained a steady temperature and 18c was a comfortable air temp and remained that way while I had the unit fitted. My car is an 04 model if that makes any difference?
Yes I am interested in your heater, I have found one in a breakers here in NI which I can try before I buy for £40, unsure if its rough or ok hence asking about faceplate swop. I'll probably go with this plan 1st as postage to NI can be expensive.
I had diagnostics carried out on my car with the vcds unit and vagcom none of which indicated any faults, the heater flaps were re-synced too.
Thank you for your very informative and detailed reply.