Our 2005 Toyota Highlander has served us well, with over 300,000 kilometres on it. The temperature dial recently stopped working and is stuck at 25 C, which is great for now but, come summer, will be problematic. The dealership has indicated that to even evaluate the problem would be a "significant cost" as removing the entire dash would be required. – Adam
I would like to suggest an alternative repair path, as I suspect the problem may not be buried deep within the dash but within the readily accessible heater control head module.
A locking nut located behind the temperature control knob is known to work itself loose after years of service, permitting the temperature control assembly to rotate back and forth as the driver twists the heater knob.
This unintended motion will tug on and ultimately damage a small ribbon wiring harness, breaking the wires where they meet the circuit board.
Disassembling and repairing this control panel is not a typical dealer repair, and many general repair shops will also hesitate, preferring to replace the whole head unit at a significant cost.
These repairs require patience and a steady hand but offer a high level of personal satisfaction.
Seek out a local automotive repair shop that specializes in electrical repairs, as they will have the necessary tools and skills for a reasonably priced solution.