Hi Greg,?
there are two fans in the 847. The one on the rear panel runs continuously. The larger internal fan only becomes active in TX. Neither of them have any form of temperature control.
Most of the noise from the rear fan comes from the fact it blows air against a circuit board. If the fan is unscrewed from the radio, it becomes much quieter.?
One thing to note. The internal fan blows against the rear of front panel, and any dust tends to accumulate there. For the benefit of all owners, it is worth taking the cases off and? checking, and blowing any dust out. I have seen one with a 1/2" carpet of dust in front of the fan.?
?
Andy Bosworth