Portable or window Honeywell air conditioner stops cooling and displays E1 on the control panel.

Safety first: Unplug the air conditioner from the wall outlet before removing any covers. Do not work on the unit while it is connected to power.

Steps to check and correct:

• Power reset: Unplug the unit for 5–10 minutes, then plug it back in and power on. If E1 clears and does not return, it may have been a temporary logic fault.
• Access the front panel: Remove the front grille or filter cover (usually no tools or a Phillips screwdriver). Locate the small sensor probe near the air intake grille or evaporator coil; it is usually a small metal or plastic-tipped probe on thin wires.
• Inspect the sensor wiring: Look for broken, pinched, or cut wires leading from the sensor to the control board. If the insulation is damaged or the wire is severed, the sensor harness must be replaced.
• Check the connector: Follow the sensor wires to the main control PCB. Ensure the plug is fully seated and not corroded. Reseat the connector several times to clean contacts.
• Test the sensor (if you have a multimeter): With the unit unplugged, disconnect the sensor and measure resistance across the two leads. A typical Honeywell NTC thermistor will show several kΩ at room temperature and change smoothly when warmed or cooled. Infinite (open) or 0 Ω (short) indicates a bad sensor.
• Replace the sensor: If the sensor is open/shorted or physically damaged, order a compatible Honeywell room temperature sensor/thermistor for your model and swap it in, routing the wires exactly as original.
• Control board check: If a known-good sensor still gives E1, the sensor input on the main control board may be defective. In that case, replacement of the main PCB is recommended and is usually best done by a qualified technician.