Honeywell air conditioner displays E3 and compressor will not start or stops shortly after starting.

Safety: Unplug the unit. Allow the unit to cool for at least 15–20 minutes if it has been running, as the condenser area can be hot.

Steps:

• Reset: After cooling, plug back in and test. If E3 persists, continue.
• Access the condenser section: Remove rear or side panels to expose the warm condenser coil and fan. Refer to the model-specific manual for screw locations.
• Locate the condenser sensor: It is usually clipped to the condenser tubing or fins near the compressor discharge line.
• Inspect sensor and wiring: Check for melted insulation, brittle wires, or a sensor that has come loose from the coil. Reattach with a proper clip or high-temperature aluminum tape if it has fallen off.
• Check connector at PCB: Reseat the connector and inspect for discoloration or corrosion.
• Test sensor resistance: With power disconnected, measure resistance and compare to expected NTC values or to another similar sensor in the unit. Replace if open/shorted or if resistance does not change with temperature.
• Replace faulty components: Install a new Honeywell condenser thermistor if needed. If E3 remains with a known-good sensor, the main control board likely needs replacement by a professional.