Display shows E3, compressor may not run or unit cycles off prematurely.

Safety first: Unplug the air conditioner. If it is a window or through-the-wall unit, be careful not to let the chassis fall when sliding it out of the sleeve.

Steps to troubleshoot E3:

• 1. Remove chassis (if applicable): For many Koldfront through-the-wall units, pull the chassis out of the wall sleeve after removing front screws. For window units, remove the front cover and any retaining screws to access the condenser section.
• 2. Locate the outdoor sensor: Find the small probe attached to the condenser coil (the hot, outdoor coil) or near the outdoor air intake. It will have two thin wires leading to the control board.
• 3. Inspect sensor and wires: Check for corrosion, broken insulation, or rodent damage. Ensure the sensor is firmly clipped to the coil or bracket.
• 4. Reseat connector: Follow the wires to the control board and unplug/replug the connector.
• 5. Measure resistance: With the unit unplugged, disconnect the sensor and measure resistance with a multimeter. Compare to the room sensor if they are the same part number. An infinite or near-zero reading indicates failure.
• 6. Replace sensor: Install a new Koldfront-compatible outdoor/condenser thermistor and secure it in the same location.
• 7. Board diagnosis: If E3 persists with a known-good sensor, the main control board is likely defective and should be replaced by a technician.