Acrid Burnt Odor - W126
 

After the last snow/freeze I left the car idling in the driveway for 15 minutes before de-icing the windows. When I got in there was a strong burned electrical smell, and I noticed the wiper switch was in the | (intermittent) position. The wipers were still imbedded in ice and not moving, but when I freed them they worked fine.

Everything else in the car is working, but now whenever the ACC fan comes on, there's the same smell.

Did I partially burn the wiper motor, and would that cause a smell inside the car? Any other clues?

Check your Mono Valve ASAP and your Aux Water Pump. Unplug them both NOW! These fail (freeze up(not weather)and will smoke your ACCU. That smell is your ACCU Unit frying. You will still get defrost air with the monovalve unpluged(you can't turn it off) and the AWP just circulates hot water in traffic and you probably won't even notice the AWP not working.
And why didn't you pop those wipers loose or did you accidentally manage to twist the wipers on? BAD RAYMR, Bad, Bad RAYMR! (been there and done that and have a burnt ACCU to prove it...same model car too.

I'll check those 2 items, thanks. Is the damage immediate, or do I maybe get some leeway? I've already driven at least an hour that way.

The wipers were somehow left on from the night before.

I would unplug them both ASAP or sooner. You can check them unplugged. The AWP plug is right next to the battery towards the drivers side, mine is held with a clip, unplug and the lead that goes down to the AWP can be checked with alligator clips attached to a wire(I made mine 3 Ft. long jsut cause I could.) and a continuity checker, clip the alligator clip one to the ground of the battery and one to the ground pin end of the AWP(brown w/tracer wire) and then clip the continuity checker to the hot pin and then touch the probe to the hot side of the battery. If the AWp is good it will spin and you can hear it running. I'd check for amperage too as they can still run and draw lots of amps.
Either a dead short or drawing lots of amps is the cause of the burning of the traces.
Do the same with the hot and ground pins of the mono valve. I believe this just opens and closes but you should hear a click if it is working. It should click on and off with the power on and off when power is removed. It too, can draw a lot of amps if going bad or be a dead short if frozen.
My car is a year older than your and is the same model.