Carel E2

What does Carel E2 mean?

The E2 alarm on Carel ir33 and pCO-based refrigeration controllers indicates that probe S2 has failed or is disconnected. S2 is typically configured as the defrost termination probe (measuring evaporator temperature) or as an auxiliary temperature probe. When the controller cannot read a valid signal from S2, it disables defrost termination by temperature and may shut off connected outputs based on configuration.

Symptoms

• E2 flashes on the controller display alternating with the temperature reading.
• Defrost termination by probe temperature is unavailable; defrost runs on time limit only.
• Controller outputs (compressor, fans) may change state depending on F0 configuration.
• Alarm relay activates and buzzer sounds.

Common causes

• Probe S2 wiring open-circuit at the sensor element or at the controller terminal.
• NTC sensor element failed (typically reads open-circuit or short-circuit).
• Probe cable routed near inductive loads, causing signal interference.
• Moisture ingress into the probe body or terminal connection causing corrosion.

Diagnostic steps

1. 01

   Inspect S2 probe wiring at the controller

   Check the S2 terminal screws on the ir33 terminal block. Confirm the conductors are fully inserted and the screws are tight.

2. 02

   Measure probe S2 resistance

   Disconnect the probe from the controller and measure resistance across the two leads. A healthy NTC at 0 °C reads approximately 6 kΩ; open or short indicates a failed probe.

3. 03

   Trace the cable along its full length

   Inspect the cable for pinch points, cuts, or areas where it runs parallel to power cables. Reroute if necessary to maintain at least 3 cm separation.

4. 04

   Replace the faulty probe

   Install a Carel-compatible NTC replacement and re-secure it to the evaporator in the same location as the original probe.

5. 05

   Reset and verify

   Power-cycle the controller and confirm E2 clears within 30 seconds. Verify the S2 temperature reading is plausible for current evaporator conditions.

When to call a professional

If E2 persists after probe and wiring replacement, the analog input on the controller board may be damaged. Contact a qualified Carel service technician to test the board input and replace the controller if confirmed faulty. Do not attempt to bypass the probe fault by rewiring, as this disables defrost protection and risks evaporator icing and compressor liquid slugging.