Carel E4

What does Carel E4 mean?

The E4 alarm on Carel ir33 and pCO refrigeration controllers signals a fault on probe S4, the fourth temperature input. S4 is commonly configured as an additional evaporator probe, a product temperature probe, or a secondary zone sensor. When S4 fails, any control or alarm function relying on it is disabled, and the controller generates this alarm to notify the technician.

Symptoms

• E4 alternates with the temperature reading on the controller display.
• Control functions assigned to S4 — such as secondary zone alarms — are disabled.
• Alarm relay output activates.
• Auto-reset occurs once a valid probe signal returns.

Common causes

• Open-circuit in the S4 probe cable or sensor element.
• Short-circuit across the NTC probe element.
• Loose wiring at the S4 controller terminal.
• Incompatible probe type (PTC vs. NTC) connected to the S4 input.

Diagnostic steps

1. 01

   Check S4 terminal connections

   Inspect the S4 terminal screws on the controller and confirm the probe wires are fully seated with the screws tight.

2. 02

   Measure probe resistance

   Disconnect S4 and measure resistance. A healthy NTC at 20 °C reads approximately 10 kΩ; open-circuit or zero resistance confirms a failed probe.

3. 03

   Inspect the cable routing

   Trace the S4 cable along its full path and look for damage, tight bends, or areas running adjacent to power cables.

4. 04

   Replace the probe

   Install a compatible Carel NTC probe and connect securely to the S4 terminals. Ensure probe type matches the S4 input configuration.

5. 05

   Reset and verify

   Power-cycle or reset the controller. Confirm E4 clears and S4 reads a plausible temperature value.

When to call a professional

Contact a qualified Carel technician if E4 persists after probe and wiring replacement, as the S4 analog input on the controller board may be damaged. Board replacement and full parameter recommissioning should only be performed by someone familiar with the Carel configuration environment.