Unit stops cooling and displays E1 on the control panel; buttons may still respond but compressor will not run.

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

Steps to check the room temperature sensor:

• 1. Power reset: Unplug the unit for 5 minutes, then plug back in and try again. If E1 returns, continue.
• 2. Access the front panel: Remove the front grille and filter. On many Frigidaire window units, the room thermistor is clipped near the evaporator coil or behind the air intake grille.
• 3. Inspect the sensor: Look for a small probe with two wires going to the main control board. Check for broken, pinched, or corroded wires and loose connectors. Reseat the connector firmly.
• 4. Test resistance: With the unit unplugged, disconnect the thermistor from the board and measure resistance with a multimeter. At room temperature (~77°F / 25°C), most Frigidaire NTC thermistors read around 10kΩ (check your service manual for exact spec). If reading is open (OL) or near 0Ω, the sensor is bad.
• 5. Replace if defective: If the thermistor is out of spec or physically damaged, replace it with a Frigidaire-compatible room temperature sensor. Route the new sensor in the same location and clip it securely away from the coil fins.
• 6. Check the control board: If a known-good sensor still triggers E1, the main control board sensor circuit may be faulty and the board will need replacement.

When to call a technician: If you are not comfortable using a multimeter or accessing internal wiring, or if the control board appears damaged (burn marks, melted spots), contact a qualified HVAC/appliance technician.