12V DC Overvoltage Protection
Assuming a brushed motor -

You likely don't need an 'overvoltage' protection, but you probably do need some sort of flyback diode and a small capacitor across your motor terminals.

When your momentary switch to your motor opens up, you will likely get an inductive kick-back which needs to go somewhere.  The diode provides that path.

One final note, in most air systems that are radial in nature (your computer fan is axial), if there is a vacuum, the load actually decreases.