Display shows E2 and temperature readings are erratic or the unit overcools/undercools.

Safety warning: Always disconnect power before opening any panels.

Steps:

• Confirm the code: Verify that E2 appears consistently and not just during startup.
• Locate the ambient/upper sensor: On single-zone hOmeLabs units, this may be near the top of the interior side wall. On dual-zone models, E2 often refers to the upper zone sensor, usually clipped behind the upper evaporator cover.
• Remove interior trim: Take out the shelves and gently remove the plastic cover where the sensor is mounted. Look for a small probe or plastic-encased sensor with two wires.
• Inspect wiring: Check for frayed insulation, pinched wires near the door frame, or moisture intrusion. Repair minor insulation damage with electrical tape; replace the harness if conductors are broken.
• Check connector at control board: Access the rear lower panel, locate the main control board, and find the connector labeled for the upper/ambient sensor. Unplug and replug it to ensure a solid connection.
• Test with a multimeter: Measure resistance of the sensor at room temperature. Compare to the expected NTC curve (typically 5–10 kΩ at 77°F). If reading is far off, open, or shorted, the sensor is defective.
• Replace sensor: Install a new hOmeLabs upper zone/ambient temperature sensor, routing the cable along the original path and securing it away from moving parts and sharp edges.
• Power up: Reassemble panels, restore power, and verify that E2 is cleared and temperature readings stabilize.

Note: Persistent E2 with a known-good sensor suggests a faulty main control board.