You'll need to open up the top motor unit, check the switch for the suction and test the fan itself. My model 1672 ran for many years, but recently it started to smell burnt when the fan was on. When I opened it up, you could see the fan spitting out sparks. I suspect the brushes are gone.
Here are instructions for opening up the motor unit. Don't pry up on the very top disk, which is an air outlet. It will only break off and won't allow access
to anything. If you do break it off, drill holes through the four posts and use stainless steel screws to re-attach the disk to the plastic posts it sits on.
Now, beneath the air outlet is the rest of the motor unit. The motor unit consists of three pieces. The bottom piece is the lid to the waste water receptacle. It is concave pointing down (lid shaped). The top piece is the domed lid for the motor unit. The middle piece is a flat plate between the other two pieces. The top of the flat plate (inside the unit) has mountings for the suction fan and the pump.
The flat plate is bolted to the bottom piece and the top piece (domed lid) is simply snapped down to the flat plate. If you take a flashlight and look inside the area where the AC cord is stored, you can see that the domed lid is a distinct piece from the flat plate. The model 1672 and 1680 (or 1680-3 if you wish) are nearly identilcal.
To access the internal parts in the motor unit, you cannot pry between bottom piece and the the flat plate because they are bolted together. But you can remove the top domed lid. To remove the domed lid, position the motor unit in front of you with the switches at 9 o-clock. Three snap-downs which attach the domed lid to the flat plate are at 1 o'clock, 2:30, and 7 o'clock. Wedge a flat bladed screwdriver or pocketknife between the edge of the domed lid and the flat plate at those locations and the lever the domed lid out and then up. The domed lid will separate from the bolted-together flat plate and bottom piece.
Wiring from the switches remain attached to to the electrical components. You will see that the AC cord has white, black, and green wires. The green ground wire connects to the fan ground at the 9 o'clock position. The white power
connects to upper connector on the pump and also to the fan at the 7:30 position. Black feeds both switches on model 1672 and then a black wire runs from the correct switch to the bottom connector on the pump or to the connector on the fan at the 1:30 position.
If you need to replace the fan, shop around carefully. The pump, for example, can be found for $30 plus shipping
, but some will want to charge you $80.