you will need to know if you have an early or late m9000. mine is the late (2006) and doesn't look just the same as what is pictured in the WSM.
appears from pictures in the book that the early evap. housing was a light color and mine, later type, is black. HOWEVER procedure looks to be about the same.
remove cab top, remove a/c coolant lines, heater hose, wire plugs as required and remove the top half of the evap. housing thereby exposing cap. tube and evap. core. route the new cap tube with switch as before and put it back together.
mine needs a new thermostat also. i wired around my switch with a single pole toggle switch. with the switch in the on position it will make the system "think" the thermostat is calling for the compressor to engage. i leave it in the on position until the air volume starts to reduce (freezing up) at this point i turn the switch to off until the air volume goes back to normal (about 3--5 min) and repeat the process all day if needed.
i would repair mine like i should if i weren't so lazy. i just don't want to discharge the freon (134a) and the heater hose...hope this helps some.
if you have more questions it might be better to pm me after you post so i will be sure to see it in a more timely manor.......al