Indoor unit shows E2 and system stops cooling or runs with poor temperature control

Safety: Shut off power to the indoor unit at the breaker and confirm no power is present before touching wiring.

Steps:

• Open the indoor unit: Remove the blower/coil access panel on the Comfortmaker air handler or fan coil.
• Locate the evaporator sensor: It is usually clipped to the evaporator coil tubing near the middle or outlet side, with two small wires leading back to the PCB (often labeled PIPE or COIL SENSOR).
• Check mounting: Ensure the sensor is firmly clipped to the coil and not hanging loose. Re-clip it tightly to clean copper tubing.
• Inspect wiring and connector: Look for corrosion, broken insulation, or a loose plug at the control board. Reseat the connector.
• Measure resistance: Disconnect the sensor and measure resistance with a multimeter. Compare to Comfortmaker's thermistor chart (NTC type). Replace if open, shorted, or far out of spec.
• Clean coil area: If the coil is heavily iced or dirty, allow ice to melt, then clean the coil fins with a coil cleaner to ensure accurate sensing.
• Reassemble and test: Reinstall panels, restore power, clear the code by cycling power, and run the unit. Monitor for reoccurrence of E2.

Call a pro if: Sensor tests good but E2 remains, indicating a possible indoor PCB failure.