00 LS400 AC fan will not reach max output
 

this is my wifes car with the NAV screen as radio/climate/etc. The fan speeds seem to work properly as you move up through the differnt fan speed levels except when you reach the 5th speed option, it seems to be the same as the 4th. Any ideas of how to fix?? Max fan is needed in texas in august.

Get a new fan. The fan in my '97 started making squealing soudns recently, so I replaced it and now it works fine. I just used the one they had in Advance Auto Parts. It works great!

first you better check your cabin air filter, just pull it out and see if you have the high speed, if you do , go get a new one, if not, put it back in, and hope someone else offers a suggestion.

Checking your air filter is a good idea, but even with a clogged air filter, you should be able to at least hear a difference in the fan when it changed from the 4th to 5th speed settings.

My guess it's the blower motor resistor that has gone bad.