2010 E550 Sedan - Rear A/C Issue
 

So my front A/C system is blowing ice cold under LO setting, but the rear A/C system isn't cold at all under LO setting.

It seems like it's just blowing warm air and recirculating the outside air. Does the rear A/C have their own condenser, or what could be possible faults?

Not sure where to start as I've gotten results searching that varies from actuator to a failing heater core.

:beat:

Run both front driver and passenger temp controls up as high as they will go to "HI" and then back down to like 70. Does the rear air come out cool then? If it does how long does it stay cool before warming up again.

The rear air doesn't not have it's own temp/blower control in the sedan as far as I know. I agree that you should adjust the temp and vent modes and see if/how it changes.