The “Liquid Line” Blindness
The C4 Error refers to a specific sensor in your Indoor Unit: the Liquid Pipe Thermistor (R2T). This sensor monitors the temperature of the refrigerant entering the evaporator coil.
Why it matters: This sensor helps the Inverter PCB decide how much to open the expansion valve. If it fails (reads too high or too low), the AC cannot control the cooling cycle efficiently and shuts down to prevent liquid flood-back to the compressor.
1 DIY Visual Checks
The “Rat Bite” Check
Open the front panel. Look at the wires on the right side connecting to the coil. Rats love the insulation on these sensor wires. 80% of C4 errors are cut wires.
Loose Connector
Did you recently have the AC serviced? Sometimes technicians accidentally pull the sensor jack loose from the PCB while cleaning.
Water Damage
If water leaks internally onto the sensor head, it can cause a “Short Circuit” reading, triggering C4. The sensor head must be dry.
Atlas Aircon Repair Protocol
Correct Sensor Replacement Steps:
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01.
Resistance Check (Ohms) We unplug the sensor and test it with a multimeter. A healthy Daikin Liquid Pipe sensor usually reads around **20kΩ** (at 25°C). If it reads infinity (Open) or 0 (Short), it’s dead.
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02.
Harness Replacement If rats have chewed the wire too close to the sensor head, we replace the entire sensor assembly. Soldering is a temporary fix; replacement is permanent.
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03.
Placement & Thermal Paste We ensure the new sensor is inserted deeply into the copper holder and apply thermal paste for accurate temperature reading.
Estimated Repair Cost (Atlas Aircon)