Hi People,
My sons 1988 300TE is showing all the signs of needing a Climate control resolder.

Sometimes blows hot, out of defrost and side vents when you need cold.
High fan speed selected and functioning then suddenly nothing.
Low speed then nothing
Switching to defrost will sometimes restore it to working, othertimes a slap in the side of the console or facia will get it going again.

So, it looks like dry solder joints.
I have searched a few times and have a basic idea, but just wanted to ask based on the above which joints to solder that may fix the problems?

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2009 Mercedes ML320 Bluetec