Carel E024

What does Carel E024 mean?

E024 in the Carel µChiller system refers to the EVD (Electronic Valve Driver) low superheat alarm on circuit 1. When the EVD driver on circuit 1 detects that suction superheat has remained below the LowSH protection threshold for longer than the E024-configured alarm delay time, the controller generates this fault. Low superheat indicates refrigerant liquid is present in the suction line, creating a risk of liquid return to the compressor.

Symptoms

• Circuit 1 fault alarm active with compressor shutdown depending on severity setting.
• EVD driver display shows LowSH protection active.
• Superheat reading on the EVD display is near zero or negative.
• Suction line may show signs of frosting near the compressor inlet.

Common causes

• Electronic expansion valve opening too far, allowing excessive refrigerant flow.
• Low superheat protection threshold set too high relative to actual operating conditions.
• Refrigerant overcharge increasing liquid refrigerant available to the evaporator.
• Pressure probe S1 faulty, causing the EVD to miscalculate superheat.
• Suction temperature probe S2 faulty, producing an incorrect low-temperature reading.

Diagnostic steps

1. 01

   Check EVD driver display for superheat value

   Access the EVD driver display on circuit 1 and read the current superheat value. Confirm whether actual superheat is genuinely low or if a probe fault is causing a false reading.

2. 02

   Verify pressure probe S1 and temperature probe S2

   Check probe connections and measure outputs. A faulty S1 or S2 probe causes incorrect superheat calculation. Replace any probe showing an out-of-range signal.

3. 03

   Review LowSH threshold and alarm delay parameters

   In the EVD driver service menu, check the LowSH threshold (should be below the superheat setpoint) and the E024 alarm delay time. Adjust within recommended limits if set incorrectly.

4. 04

   Check for refrigerant overcharge

   Monitor suction superheat and subcooling with service gauges. Excessive subcooling alongside low superheat points to refrigerant overcharge, which requires partial refrigerant recovery.

5. 05

   Inspect expansion valve operation

   Put the EVD into manual control mode and observe superheat response to valve position changes. A valve stuck open requires stator resistance testing (expect approximately 36 ohms per winding) and possible stator or valve replacement.

When to call a professional

Liquid refrigerant returning to a compressor causes severe mechanical damage within minutes. Call a licensed technician immediately if superheat is confirmed low and the cause is not resolved by probe verification or parameter adjustment. Refrigerant recovery for charge correction or valve replacement requires EPA 608 or equivalent certification and specialized recovery equipment.