Carel E3

What does Carel E3 mean?

The E3 alarm on Carel ir33 and pCO-based refrigeration controllers signals a fault with probe S3, the third temperature input. S3 is often configured as a condenser temperature probe, a secondary cabinet probe, or an auxiliary measurement point. When S3 fails, any control or alarm function relying on this probe — such as condenser fan speed control or high condenser temperature alarm — is disabled.

Symptoms

• E3 alternates with the current temperature on the controller display.
• Functions controlled by S3 (e.g., condenser fan modulation, auxiliary alarm) stop operating correctly.
• Alarm output activates.
• The alarm auto-resets once a valid probe reading returns.

Common causes

• Open-circuit or short-circuit in the S3 probe element.
• Loose or corroded wiring at the S3 terminal on the controller.
• Probe cable damage along the routing path.
• Incorrect probe type connected to S3 (PTC vs. NTC mismatch).

Diagnostic steps

1. 01

   Check S3 terminal connections

   Confirm the S3 wiring is properly seated and screws are tight at the controller terminal block.

2. 02

   Measure S3 probe resistance

   Disconnect and measure across the S3 probe leads. An NTC at room temperature (20 °C) reads approximately 10 kΩ; verify against the probe datasheet specification.

3. 03

   Inspect the cable routing

   Ensure the S3 cable is not routed with power or inductive cables and has no visible damage or pinch points along its length.

4. 04

   Replace the probe if defective

   Install a compatible Carel NTC probe in the same mounting location and connect to the S3 terminals securely.

5. 05

   Verify probe type compatibility

   Confirm the replacement probe type (NTC or PTC) matches the controller's S3 input configuration parameter setting.

When to call a professional

Escalate to a licensed refrigeration technician if S3 drives condenser fan control and the condenser is running at unknown speed, risking high-head pressure. A technician should also be contacted if probe replacement does not clear E3, as this indicates a controller board analog input fault that requires board replacement and professional parameter recommissioning.