Heat/Cool selector valve - dash

'98 4runner, 4 banger, auto tranny. The heat/cold selector knob won't rotate but about one quarter around from cold to hot on the graduated color scale. Just won't rotate any further. How easy is it to replace this thing? Has anyone else's $%@! the bed like mine has?:runaround:

The knob controls a valve on the firewall in the engine bay. Try moving it by hand while someone turns the knob. The valve has 2 heater hoses running to it.