Unit runs briefly then stops; display shows E1 and beeps; some models may not respond to mode changes.

Safety first: Unplug the air conditioner from the wall outlet before removing any covers. Capacitors inside can hold a charge; avoid touching exposed terminals.

Steps to check and address E1:

• 1. Power reset: Unplug the unit for 5–10 minutes, then plug back in and try again. Sometimes E1 is triggered by a transient fault.
• 2. Access the front control area: Remove the front grille and filter. On most Insignia window units, the room thermistor is clipped near the evaporator coil behind the front panel, with two small wires leading to the control board.
• 3. Inspect the thermistor: Look for a small probe or bead sensor attached to the evaporator fins. Check that it is firmly clipped in place and not dangling or touching the plastic housing. Re-seat it if loose.
• 4. Check wiring and connector: Follow the thermistor wires to the main PCB (control board). Ensure the plug is fully seated, not corroded, and that no wires are pinched or broken. Reseat the connector several times to clean contacts.
• 5. Basic resistance test (for advanced DIYers): With the unit unplugged, disconnect the thermistor from the board and measure resistance with a multimeter. At room temperature (around 77°F / 25°C), most Insignia NTC thermistors will read between 5–20 kΩ. A reading of 0 Ω (short) or infinite (open) indicates a bad sensor.
• 6. Replace if defective: If the thermistor is open/shorted or physically damaged, replace it with an Insignia-compatible room temperature sensor for your exact model. Route the new sensor wires along the original path and secure them away from the fan blade.
• 7. If E1 persists: If a known-good thermistor is installed and wiring is intact, the sensor circuit on the main PCB may be faulty. At this point, replacement of the main control board is recommended and is best handled by a qualified technician.