hello,
odd problem you have there! ....do the led lights on the heater control panel buttons flash when you first start the car? if they do then there is a fault code recorded in the climate control module (assuming you have auto air con.)
having a dealer read these faults would give an idea of the problem.
two common problems on old v70's are worn out fan motor which draws too much current and stops working intermittantly, and faulty fan power stage module.
i cant think how any fan problems would relate to the brake pedal but cars are like that sometimes...

steve.