How to Fix / Troubleshooting

Safety first: Shut off power to the indoor unit at the breaker and verify power is off before removing access panels.

Step 1 – Access coil area: Remove the blower/coil access panel on the air handler or furnace cased coil.
Step 2 – Locate coil sensor: Find the small probe or clip-on thermistor attached to the evaporator coil tubing or fins, connected by two small wires to the control board.
Step 3 – Inspect and reseat: Check that the sensor is firmly attached to the coil and that its wiring is not cut or pinched. Reseat the connector on the control board.
Step 4 – Test sensor: With power off, disconnect the sensor and measure resistance. Compare to Keeprite specifications for the coil sensor. Replace if open, shorted, or far out of range.
Step 5 – Reassemble and test: Reinstall the sensor, secure wiring away from sharp edges, close the panel, restore power, and run the system. If E3 remains, the indoor control board may need replacement by a professional.

Keeprite indoor display shows E3 and cooling stops; outdoor unit may not run.

Possible Causes