How to Fix / Troubleshooting

Safety first: Turn off power at the breaker and wait a few minutes for capacitors to discharge.

Steps:

Locate coil thermistor: Remove the front cover and access panel. The coil thermistor is usually clipped to the evaporator coil tubing or fins.
Check mounting: Ensure the thermistor is firmly attached to the coil in the correct position. Reattach with the original clip or a new clip if it has fallen off.
Inspect wiring: Follow the thermistor wires back to the PCB. Look for pinched, cut, or corroded wires. Repair or replace as needed.
Test resistance: Disconnect the thermistor and measure resistance at room temperature. Compare to the service manual chart. Replace if open, shorted, or significantly out of range.
PCB evaluation: If a new thermistor does not clear E3, the indoor PCB may not be reading the sensor correctly and should be replaced by a technician.

Indoor unit stops cooling/heating, E3 displayed, may stop shortly after startup

Possible Causes