Unit will not start cooling, display shows E1 shortly after power-on.

Safety first: Unplug the Klarstein air conditioner from the mains before opening any panels. Do not work on live circuits.

Steps to check and fix:

• Power reset: Disconnect power for 5–10 minutes, then reconnect and test. Sometimes E1 is a temporary sensor read error.
• Locate the room sensor: On most Klarstein portable and wall units, the room NTC sensor is clipped near the front air intake grille or on the evaporator coil frame, connected by two thin wires to the main PCB.
• Inspect wiring: Check the sensor wires and connector for cuts, pinches, or corrosion. Reseat the connector on the main PCB firmly.
• Measure resistance: With the unit unplugged, disconnect the sensor and measure resistance with a multimeter. Typical NTC values are around 5–20 kΩ at room temperature (check Klarstein service data if available). If the reading is open (infinite) or near 0 Ω, the sensor is defective.
• Replace sensor: If faulty, replace with a compatible Klarstein room temperature NTC sensor assembly. Route the new sensor in the same position and secure it with clips or tape away from direct airflow obstructions.
• Check main PCB: If a known-good sensor still gives E1, the sensor input circuit on the main control PCB may be defective and the PCB will need replacement.

When to stop: If you are not comfortable using a multimeter or accessing the control board, contact a qualified technician.