Pressure faults are one of the most common causes of chiller shutdowns. Whether high or low, they usually indicate a deeper issue with heat transfer, fluid flow or refrigerant charge. If left unaddressed without a rapid repair, they can lead to recurring alarms, reduced cooling performance or long-term equipment damage.
This article explains the difference between high-pressure and low-pressure faults in modern cooling systems, what causes them and how they should be diagnosed and resolved.
Understanding Pressure Control in Chillers
All chiller units rely on a controlled pressure cycle to function efficiently. The refrigerant passes through a closed loop, evaporating at low pressure to absorb heat and condensing at high pressure to release it. Maintaining the correct balance between these stages is essential for stability.
To protect critical components, most well-designed chiller systems are fitted with pressure sensors and safety switches. These monitor suction and discharge pressures and will trigger a fault or shut down the system if conditions fall outside safe limits.
What Causes High-Pressure Faults?
A high-pressure fault occurs when the system’s discharge pressure rises above the manufacturer’s threshold. This is typically linked to a problem on the condenser side, where heat should be expelled. Common causes of high-pressure faults include:
- Blocked or dirty condenser coils that reduce heat rejection
- Poor airflow across air-cooled condensers due to failed fans or obstruction
- Water flow issues in water-cooled systems, such as closed valves or scale buildup
- Overcharging of refrigerant leading to increased head pressure
- High ambient temperatures which lessen heat rejection
High-pressure faults are usually accompanied by increased compressor load and head pressure readings. Some systems may continue operating at reduced capacity before shutting down.
What Causes Low-Pressure Faults?
Low-pressure faults occur when suction pressure drops below a safe threshold. This can cause refrigerant to boil at too low a temperature or the compressor to operate in a vacuum, both of which are damaging over time. Typical causes include:
- Refrigerant undercharge due to a leak or improper filling
- Frozen or fouled evaporators from low airflow or poor circulation
- Restricted expansion valves or blocked strainers
- Low load conditions leading to excessive cycling
- Sensor drift or calibration faults causing false alarms
Unlike high-pressure faults, low-pressure issues are more likely to develop gradually but still lead to trips or underperformance.
When a pressure fault is detected, the first step is to confirm whether it is a genuine condition or a sensor issue. Pressure transducers can drift, and wiring faults can cause false readings.
Once the fault is verified, engineers check the temperature-pressure relationship to confirm refrigerant charge. They inspect the condenser and evaporator for blockages and measure airflow and water flow through coils and heat exchangers. Expansion valves, pressure switches and fan controls are tested for correct response. Recent maintenance should also be reviewed, as changes in configuration can introduce faults.
It is important not to reset the system and resume operation without identifying the root cause. Otherwise, the fault will probably simply return.
How to Prevent Pressure Faults
Most pressure-related problems can be prevented with routine maintenance and proper design. Key measures include:
- Cleaning coils at regular intervals
- Checking refrigerant levels and logging pressure readings
- Verifying fans, pumps and valves are operating correctly
- Ensuring the system is correctly sized for its application
Modern chillers are designed to shut down when conditions become unsafe, but relying on these fault limits is not ideal. Preventative maintenance reduces wear on components and helps maintain long-term efficiency. This is why the regular servicing of chiller units is so beneficial, of course.
Final Thoughts
In the final analysis, both high-pressure and low-pressure faults are clear signs that a chiller is no longer operating within its intended design range. While their causes differ, both require prompt investigation to avoid lasting damage.
If your system is experiencing repeated faults, it may be time for a full inspection or system health check. Understanding the cause is the first step to restoring stable, reliable cooling. Feel free to get in contact with our expert team to discuss potential pressure faults your system may currently be experiencing. We can advise you on appropriate countermeasures and, if necessary, offer you new and reconditioned chillers to replace your current system.
