Daikin indoor unit displays C9; poor temperature control or the unit stops.

Safety first: Turn off power before removing the front panel.

Steps:

• Locate the room thermistor near the air intake grille; ensure it is not hanging loose or touching cold surfaces.
• Check that the sensor connector is firmly attached to the PCB.

Technician actions:

• Measure the resistance of the room thermistor and compare it with Daikin's temperature-resistance chart.
• Replace the room thermistor if it is out of specification or physically damaged.