Although this is based on the LS400 model other models are similar and the process is the same.
The 1st thing is to ensure your AC is actually working correctly, most AC specialists will check the vent temperatures free of charge and only charge if further work is required.
Expect to pay around £40-£60 for a top up of refrigerent from a professional outfit, the process is normally fully computer controlled.
All AC specialists now have to be registered so make sure they have the necessary certificate to do the work.
Looking good so far.
Once you have your AC in good working order the next thing is to check your pollen filter (the early LS400 1990-1992 did not have a pollen filter fitted so owners of this model please pass this section)
These are normally located in the passenger side footwell,in the 1994-1994 LS400 it is located by removing the kick panel, look up and you will see a cream coloured box with 2 wing nuts.Remove the wing nuts and the panel.The 2 filters are located inside the box.Slide the filters back then pull out.
On the later LS400 and GS300 the filter is located at the back of the passenger lower glove box, at the rear there is a cover remove the cover and you will see the filter housing, unclip the cover and remove.Pull the complee filter and housing out.
Replacement filters are around £20.00-£40.00 some are only available OEM some are aftermarket.
The filters can be cleaned with compressed air but generally replacement will give better results.
The one below is typical of a neglected filter, removed from a 1997 LS400.
Once the AC and the filter are sorted it is now time to move onto the cleaning process. For this I am using an aerosol type cleaner commonly refered to as "The Bomb" method.
This aerosol is available at most car accessory shops or in my case at Aldi, prices vary between £3.99 - £14.99.
The basic proceedure is to start the engine, turn the AC to maximum cold,open all the air vents fully,place the can behind the front seats ( the transmission tunnel is ideal on a Lexus),activate the aerosol by pressing down the tab and locking it down,close all the doors and then wait around 10 minutes for the can to discharge.
Full manufacturer instructions will be on the product you purchase,please read and follow their recommendations.
Wait another minute or two once the can has fully discharged to allow the ventilation to purge fully then turn off the engine and open all the doors to fully ventilate.
Do not leave the AC on with the doors open as it could overload the system.
That's it, the AC and the car should now be smelling nice and fresh with the bacteria killed off.
It's recommended to do this every six months but I find once every 12 months is adequate.