AHT Cooling Systems E42 Error Code

What does AHT Cooling Systems E42 mean?

The controller reports a time-out condition with the electronic expansion valve (EEV) commanded at 100% open. Under normal operation the EEV modulates to maintain superheat; if the controller has driven the valve fully open for longer than its permitted timeout period without achieving the target superheat, E42 triggers. This indicates a severe refrigerant shortage, a blockage upstream of the EEV, or a fault in the EEV system itself.

Symptoms

• E42 fault code displayed with red LED and buzzer active.
• EEV driven to 100% open position — maximum refrigerant flow commanded but superheat remains high.
• Cabinet temperature rising above setpoint despite full refrigerant flow demand.
• Suction line may feel warm — insufficient liquid refrigerant reaching the evaporator.
• May co-occur with E34 (superheating too high) if superheat alarm threshold is also exceeded.

Common causes

• Significant refrigerant loss reducing liquid supply below what the evaporator needs at full EEV opening.
• Filter drier severely blocked, starving the EEV of liquid refrigerant.
• EEV body mechanically seized or valve seat damaged, preventing full flow despite full electrical command.
• Liquid line restriction (kinked tube, partially closed service valve) upstream of the EEV.
• EEV wiring or driver circuit fault causing incorrect position feedback to the controller.
• Loss of refrigerant subcooling due to condenser fouling, causing flashing before the EEV.

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Diagnostic steps

1. Move goods immediately

   Transfer all temperature-sensitive goods to another correctly rated cabinet — E42 indicates the refrigeration circuit is unable to meet load even at maximum valve opening.

2. Record fault and device details

   Note E42, device type, and serial number from the nameplate (Fig. 13). Contact AHT service with this information.

3. Check condenser and airflow

   Inspect condenser coils and grilles for dust and blockage. A heavily fouled condenser causes loss of subcooling, which leads to refrigerant flashing before the EEV and effectively reduces liquid supply.

4. Inspect liquid line for restrictions

   Check for frost forming on the filter drier or liquid line that would indicate a restriction or blockage. A cold/warm temperature differential across the drier confirms a block.

5. Contact AHT service

   E42 requires an AHT-authorized technician to assess refrigerant charge, filter drier condition, and EEV mechanical operation. Contact 00800/73783248 or www.aht.at/service.

When to call a professional

E42 almost always indicates a refrigerant charge issue, drier blockage, or EEV mechanical fault requiring an AHT-certified technician. On R-290 units, all refrigerant circuit work must be performed by personnel certified for flammable refrigerants. Contact AHT service at 00800/73783248 or www.aht.at/service without delay.