Welcome, Peter! Many of us (me included) have learned much of what we now know about MBs from sites like this.
What Arthur is subtly trying to tell you (not that he needs me to translate!) is to start off by searching the site. There are MANY, MANY posts on this subject, which is to say that many of us have had problems with our auxilliary fans. Fortunately, it's a simple system to diagnose and fix.
Search on "aux fans" and you'll learn a lot. Wouldn't be surprised to see some very cogent posts by Mr. Dalton (and a few by me).