Indoor unit display shows E1 and cooling stops or runs briefly then shuts down

Safety first: Turn off power to the Comfortmaker air handler at the breaker and verify the indoor fan has stopped before removing any panels.

Steps to check and correct:

• Access the indoor control compartment: Remove the front panel of the air handler or fan coil to expose the control board and sensor wiring.
• Locate the room thermistor: On most Comfortmaker split systems, the room sensor is clipped near the return air inlet or mounted on the control board with two small wires (often labeled RT or ROOM SENSOR).
• Inspect wiring: Check for broken, pinched, or disconnected wires between the thermistor and the indoor PCB. Reseat the plug firmly on the board.
• Check sensor resistance: With power still OFF, disconnect the thermistor and measure resistance with a multimeter. Compare to the service chart for Comfortmaker (typical NTC ~10kΩ at 77°F/25°C). If reading is open, shorted, or far out of range, the sensor is bad.
• Clean and reposition: If the sensor is covered in dust or touching metal, gently clean it and ensure it is in free air flow, not touching the coil or cabinet.
• Replace if defective: If resistance is incorrect, replace the room temperature sensor with a compatible Comfortmaker/ICP thermistor kit.
• Restore power and test: Reassemble panels, turn power back on, clear the code by cycling power, and run the system in COOL to verify normal operation.

When to call a technician: If the thermistor tests good but E1 persists, the indoor control board thermistor circuit may be defective and should be diagnosed and replaced by a qualified HVAC technician.