Unit will not run, display shows E1 shortly after power‑up or when trying to change modes.

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

• Power reset: Disconnect power for 5–10 minutes, then plug back in and try again. Sometimes E1 can be triggered by a transient fault.
• Access the control area: Remove the front panel or top cover (varies by model) to access the control PCB and the small thermistor probe that senses room temperature. It is usually clipped near the air intake grille.
• Inspect the sensor: Locate the small bead or bullet‑style thermistor with two thin wires going to the main board. Check for broken insulation, cuts, or a broken sensor tip. Ensure it is firmly clipped in place and not dangling in the air stream.
• Check connections: Follow the sensor wires to the main PCB. Unplug and re‑seat the connector several times to clean the contacts. Look for corrosion, bent pins, or loose fit.
• Test continuity (advanced): With the unit unplugged, use a multimeter set to resistance (ohms) and measure across the sensor leads. A typical NTC thermistor will show a resistance in the 5–50 kΩ range at room temperature. Infinite (open) or near‑zero (short) ohms indicates a bad sensor.
• Replace if faulty: If the sensor is open/shorted or physically damaged, replace it with a compatible Whynter ambient temperature sensor / thermistor for your exact model. Route the new sensor wiring along the original path and secure it away from the fan blades.
• Control board check: If a known‑good sensor still gives E1, the main control PCB may have a failed sensor input circuit and will need replacement by a qualified technician.