Rear air conditioning is a separate set of air conditioning controls and vents for rear seat passengers. Many vehicles will use the same compressor for the model with or without rear air conditioning, but the lines are different, meaning the filter dryer and expansion valve will be unique, so this is something you should pay more attention to. Complete AC Kit. It’s also worth noting that rear-conditioned vehicles have a second expansion valve for the rear, which should be taken into account when diagnosing air conditioning problems in your vehicle.