Humming Noise Under Dash
 

Today, I noticed a humming noise that seems to be coming from somewhere under my dash board. It sounds like maybe a motor or servo of some kind. When I turn the cockpit blower fan completely off, it goes away. Then, when I turn it back on (either in just fan or a/c mode) it takes a few minutes for it to reappear.

Any ideas?

Fan motor bearing my guest!

Aux. Water pump for the heater is another possibility.

Thanks. I recently replaced the blower fan and regulator, so I'll check out the aux heater pump. Does that operate without calling for any hot air? The problem occurred with the temp selector in full cold. The humming seems to be coming from under the dash, right above where the temp controller is positioned.

my guess is the little aspirator motor right behind the glove box to the right.. I draws air across the temp sensor.. Its located right under the very right hand vent. Its easy to take apart and oil up.

Bill