Started up the Rover and turned the a/c on, about a minute later white smoke and a burning smell started to come from the vents for like 30 seconds. Turned it off then started it again no smoke and the burning smell was pretty much gone. The air was also super cold like I've never felt before. Blower motor on the way out?

 

If your fan speed no longer works - It’s either on at the highest speed or off, then your fan relay just burned out. Happened to me on my Isuzu a few months ago. It was a $10 part and took 20 minutes to replace on the Isuzu. Not sure how pricey/difficult it is on a Disco.

 

Tested it and the fan speed still works so I'm not sure what happened

 

Have you tried turning the temp up and change the airflow through all the options? If it wasn’t the blower motor it’s probably an actuator for the blend doors and air direction.