Lexus 2003 LS Owner's Manual page 214

AIR CONDITIONING
(b) Rear Cooling
1. Turn the front air conditioning on. The rear cooler will not
turn on if the front air conditioning is off.
2. Turn the rear air conditioning on. The fan speed and rear
cooler are adjusted automatically.
3. Use either of the "LO HI A/C" buttons to adjust the desired
fan speed and the rear cooler. Each indicator light shows
which mode is now selected.
(c) Air Purification
The air purifier operates whenever the rear air conditioning or
the rear fan operation is on, regardless of front air conditioning
activation.
200
(d) Rear air filter
21L075
Replace the air filter when the use of rear air conditioning or air
purification function reduces air flow or deodorant
performance.