Blue Star AC Error Code E3
Diagnostic Protocol & Repair Guide
Technician Note
Always isolate power before inspecting high-voltage components.
Blue Star Error E3
Evaporator Sensor Fault.
Anti-Freeze Protection System is Down.
Part
Copper Sensor
Common Cause
Rat Bite
Fix
Replace Sensor
The “Copper Tip” Problem
The E3 Error refers to the Evaporator Coil Sensor. Unlike the black plastic E1 sensor, this sensor has a copper tip and is inserted directly into a small metal pocket welded onto the cooling pipes of the indoor unit.
Why it fails: The constant cycle of freezing cold and normal temperature causes thermal stress on the sensor. Over time, the internal resistance drifts, or the wire breaks. Rats are also attracted to the wire insulation.
1 DIY Visual Checks
Rat Damage Check
Open the front grill. Follow the wire coming from the right-hand side of the copper coil. Is the wire chewed? This is the most common reason for E3.
Sensor Dislodged?
Sometimes the copper sensor slips out of its holder. If it’s hanging in the air instead of touching the pipe, it will give wrong readings (though usually not E3, but poor cooling).
Loose PCB Jack
If the AC was moved or serviced recently, the sensor plug on the main PCB might have been pulled loose.
Atlas Aircon Repair Protocol
How we fix the E3 Fault:
-
01.
Resistance Measurement We unplug the sensor and check its Ohms. A healthy Blue Star coil sensor usually reads around **20kΩ** at 25°C. If it reads 0 or Infinity, it’s dead.
-
02.
Sensor Replacement If the wire is cut near the jack or sensor head, we replace the whole assembly. We ensure the new sensor matches the resistance curve of the original.
-
03.
Placement Verification We insert the new copper sensor deep into the holder and secure it. We often add a dab of thermal paste to ensure accurate temperature sensing.
Estimated Repair Cost (Atlas Aircon)