I replaced the HVAC control panel on my 2003 4900 recently. I'm posting this for a reference in case someone needs to do this. It's a straightforward job and all you need is a Phillips screwdriver and pliers to pull the zip tie for tools.
1) Open the hood and remove the fiberglass cowling in front of the windshield. The control cable enters the cab right behind the coolant tank.
2) disconnect the inner cable at the water valve right inside of the right side air cleaner, behind the intake hose. The push the cable through the fire wall into the cab
3) Remove the trim from the control panel, remove 4 screws, disconnecte the two wiring pigtails and the single wire that attaches to the panel. Pull the whole assembly out. Undo the center dash panel and pull it back for access. You'll need to unscrew the brake valve knobs.
4) remove the rubber grommet from the firewall and push the OLD cable into the cab from the outside.
5) feed the new cable through the hole in the dashboard for the control panel and tape the new and old cable ends together.
6) pull the new cable through the firewall from the outside.
7) the grommet was a little tight sliding over the new cable and firewall but a shot of WD40 took care of that and fitting it back into the hole.
8) very important: the business end of the cable housing must be anchored for the control cable to operate. A zip tie seems to be the factory method as far as I can tell.