Does anyone know where I can find instructions on how to remove the AV evaporator from a 1990 LS400? I haev a subscription to Alldata.com but not info there, I also have the Mitchell CD-rom manual (the sold on Ebay type), which also does not help. Any help would be greatly appreciated.

 

are you talking about the evaporator core? If so you have to take off the glove box and there is a white plastic cover that takes some doing but will eventually come off. From there you can see the evaporator. Now you have to go to the other side of the firewall to disconnect the a\c lines. It is pretty hard to get to but again it is do-able.
I just finished doing the same thing to my 92 sc400.