Indoor Heat Exchanger Thermistor Abnormality

Home Appliance Error Codes Daikin Split AC

Can you still use it? With care until repaired

Who can fix it? Needs a technician

Typical repair time 30 minutes – 2 hours

Typical cost SAR 80 to 1,200

What it means

This code appears on Daikin split, ducted and cassette air conditioners and means the thermistor on the indoor heat exchanger is reading outside a sensible range, which points to an open or shorted circuit. The unit relies on this sensor for freeze protection and cooling control, so it usually stops or runs erratically. The same code can mean something else on other brands.

Models covered: Daikin split air conditioners and Daikin ducted/cassette (SkyAir) units, which share the same error code system; the code shows on the wired remote or via the wireless remote check function.

Symptoms3

Code C4 appears and the unit stops or does not start cooling.
Erratic or on-off cooling, sometimes before the code appears.
Ice may form on the evaporator because freeze protection is no longer accurate.

Possible causes5

A loose or corroded thermistor connector on the board.
A failed thermistor from moisture or age.
A cut, chewed or pinched sensor wire.
The thermistor has slipped out of its holder on the coil pipe.
A faulty sensor input circuit on the indoor PCB.

How to diagnose5

Switch the unit off at the breaker for a few minutes and restart to rule out a one-off error.
A technician checks the thermistor connector on the board for a firm, clean fit.
The technician traces the sensor wire for cuts, pinching or corrosion.
The technician measures the thermistor resistance at a known temperature and compares it with the Daikin table for the model.
If the thermistor is good and the code persists, the board's sensor input is checked.

How to fix5

Refit the thermistor in its holder and reseat its connector.
Repair or replace the damaged wire.
Replace the heat exchanger thermistor with the correct part for the model.
Replace the indoor PCB if its sensor input is proven faulty.
Run and test the unit and confirm the code does not return.

Repair cost

0–200

200–600

600–1,500

1,500+

In Saudi riyals; the highlighted part is the expected range for this fault.

Most cases are solved by a new thermistor or a connector repair at low cost; the price only rises if the board itself has failed.

Prices are rough estimates including the part and the technician’s fee, and vary with brand, model and part source.
Prices last updated: September 2026

Frequently asked questions

What is the difference between C4 and C9?

C4 is the sensor clipped to the indoor coil pipes, while C9 is the room air sensor that reads the air entering the unit. They sit in different places with different connectors.

Is the thermistor an expensive part?

No, it is relatively cheap and quick to fit. The key is to confirm the fault is in the sensor, not the connector or board, before replacing it.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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