The fans direction is controlled by vacuum lines running from the top rear of the engine down behind the engine through the fire wall to a chamber in the drivers foot well, then out again and up to the back of the switch, it is most likely that somewhere in this series there is a leak. you can check the line coming from the engine by unplugging the hose in the drivers foot well and feeling for suction, if it's ok there then the problem is probably behind the switches and you need to pull that section of the dash off to find it. Listening for a slighting hissing/sucking noise will help you trace it as well. People being to rough when messing around with the car stereo can damage the vacuum lines where they are secured in the back.
Blockages can also occur but are less likely so keep this in mind while you are searching.
Nips, April 2008
