[rovertone]

A key point for me would be the steering going stiff and heavy and the charge light coming on which suggests that the pump and the alternator stopped turning which points to the auxiliary drive belt not turning.
Now if this happened in conjunction with the AC being switched on the compressor puts a load on to the crank pulley which if the rubber bonding to the centre is failing you will get a burning smell, in conjunction with the pulley stopping.

I have had a crank pulley fail without warning where the crankshaft was turning without the pulley hence the burning smell and no pwr steering or charging.

I also recently had an alternator pulley bearing fail that stopped the aux belt completely but that came with a few miles of noisy warning.

I would suggest running the engine at idle with AC off and watch the aux belt then switch on AC and see if the belt rotation falters as well as AC try turning the steering lock to lock which will add more load to the crank pulley.

If all seems well I would switch off and check the tension on the aux belt, perhaps the tensioner is failing which is causing the belt to slip thus intermittently stopping the steering pump and alternator again you would get a smell from belt slipping.

Hope that helps, good luck.