Heating/Cooling fan works intermittently

I have a 1998 Ford Taurus Sedan where the interior heating and cooling fan does not work all the time. It used to start working when we ran over a speed bump, or we would resort to thumping the dash right above the oval radio console. Now, we can't get it to work at all, but on its own, sometimes you can hear the fan trying to run, and then will pick up speed and run. I suppose the fan itself is shot. I have removed the radio console and checked the fan switch, and it is fine. I noticed that there was a rectangular box with wires going into it that was mounted just behind the radio console. I wondered if there was something in that box that may have a short in it that was jiggled into place when we would pound on the dash? The part number on the box is F8DB19A475-AB. I don't know, it's probably irrelavant.

Is it possible to replace the interior fan motor without removing the entire dash?

Tom