Hi everyone, I'm looking for abit of advice if anyone could help me please it would be much appreciated.

I am wanting to convert my single din head unit for a double din one on my audi a4 b7. I have been reading up on the subject and it has been advised when looking to buy a double din climate control unit the buttons must match. Is this an absolute must? because their is 1 odd button where the "Off" button used to be on the B6 model I once owned. In its place is what looks like another re-circulating air button with an "A" on it. Really don't want to have to go to a main dealer if I can help it because when I've been scanning the internet the only double din climate control units i can find for sale have the "Off" button on them.