I usually just set ~20-25C auto and just for kicks I reached over to see if the rear vents had air flow, and it didn't. What HVAC settings would cause them to turn on?

 

The thing about the rear vents is that in auto mode only the A/C blows out of the center front vents which the rear vents are tied to, so you'll get A/C in the rear. When auto switches over to heat, no air flow from the center vent, therefore no air flow from the rear vents. If you want constant flow, take it off auto mode.

 

A/C (cold) air comes through the rear vents on the center console; heated air for the rear passengers comes from vents under the front seats.

 

theres also a vent switch back there just like all the front vents have. make sure its set to open.

 

I believe it only comes on when you have the air pointing at the above seat position. When its shooting below I feel it only gets your feet area.