Unit will not run, display shows E1 shortly after power-up

Safety first: Turn the Friedrich air conditioner OFF and unplug it from the wall. If it is a built-in or PTAC unit on a dedicated disconnect, switch the breaker OFF before removing any covers.

Steps to check and correct E1:

• Power reset: Leave the unit unplugged for 5 minutes, then plug back in and power ON. If E1 returns immediately, continue below.
• Access the front sensor: Remove the front grille and filter. On most Friedrich room and PTAC units, the indoor ambient thermistor is clipped to or near the evaporator (indoor) coil or mounted behind the return air grille.
• Inspect the sensor and wiring: Look for a small probe with two thin wires going to a plug. Check for broken wires, pinched cable, or corrosion at the connector. Reseat the connector firmly on the main control board.
• Test the thermistor (if you have a meter): Disconnect the sensor and measure resistance. At room temperature (around 77°F / 25°C), most Friedrich NTC thermistors will read in the 8–15 kΩ range (check your model’s service data). If it reads open (OL) or near 0 Ω, the sensor is defective.
• Replace if defective: If the sensor is open/shorted or physically damaged, replace it with the correct Friedrich ambient thermistor for your model. Route the new sensor wiring away from sharp metal and moving parts, and clip it securely to the coil or bracket as originally installed.
• Check the control board: If a known-good sensor still gives E1, the main control board’s 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 to be the issue, contact a qualified HVAC technician or Friedrich-authorized servicer.