Coleman digital air conditioner shuts down and displays E1 on the thermostat or control board; unit may not respond to temperature changes.

Safety first: Turn OFF power to the air conditioner at the disconnect and the main breaker before removing any panels. Verify power is off with a non-contact voltage tester.

Step-by-step:

• Reset the system: Turn the thermostat OFF, cut power at the breaker for 5 minutes, then restore power and see if E1 clears. If it returns, continue.
• Locate the indoor sensor: On most Coleman split and packaged units, the ambient sensor is either in the return-air section near the indoor coil or integrated into the wall thermostat (for some RV and residential models).
• Inspect the sensor wiring: Remove the indoor access panel. Trace the small-gauge sensor wires from the sensor to the Coleman control board. Look for loose plugs, corroded terminals, or damaged insulation. Reseat the connector firmly.
• Check sensor resistance: With power still OFF, disconnect the sensor from the board. Measure resistance with a multimeter. Compare to the Coleman service chart (typically 10k–20k ohms at room temperature). If reading is open, shorted, or far off spec, replace the sensor.
• Inspect the control board: If the sensor tests good and wiring is intact, the sensor circuit on the Coleman control board may be defective. Look for burn marks or swollen components. Replacement of the board is usually required.
• Reassemble and test: Reconnect everything, restore power, clear the code by cycling power, and verify the unit responds correctly to thermostat settings.

When to call a technician: If you cannot access the sensor safely, or the control board appears damaged, contact a qualified Coleman HVAC technician.