The most common cause is a blocked or dirty condenser coil, which prevents proper heat dissipation. Dirt, debris, or clogged fins on the coil lead to heat buildup and high refrigerant pressure. Similarly, if the condenser fans are obstructed or running at reduced speed, the effect is the same.
If one or more condenser fans stopped working (e.g., fan motor failure or overload like AL366 on one fan), the remaining fans might not handle the heat load, causing pressure to rise.
Extremely hot weather can push pressures high. Also, if the chiller is too close to walls or other equipment, recirculating hot air, the condenser can't reject heat effectively, leading to an HP alarm.
Less commonly (and to be checked by technicians), having too much refrigerant in the system or air/non-condensable gases can elevate pressure. This isn't usually the first suspect unless recent maintenance involved adding refrigerant.
For safety, turn off the chiller before attempting any inspection. High pressure conditions can be dangerous, and you will likely need to access the condenser area.
Check the condenser coils for dirt, dust, or obstructions. Clear any debris and clean the coil fins gently (e.g., with a soft brush or coil cleaner). Ensure nothing is blocking airflow into or out of the coils (like leaves, paper, or other debris).
With the power back on, observe the fans when the chiller starts (or manually test them if possible). Replace or repair any non-working fan. If a fan motor overload tripped (e.g., you also have AL366 alarm), reset that as well. Balanced airflow is crucial.
If the unit is in an enclosure or near walls, open doors or create space for ventilation. In high ambient conditions, every bit of airflow helps – you might use temporary fans to augment airflow as a short-term fix, but ultimately ensure the chiller has proper clearance per manufacturer specs.
Once the underlying issue is addressed (coil cleaned, fans running), reset the high-pressure alarm. On many systems, the high-pressure cutout might be a manual reset switch on the compressor or in the electrical panel that needs to be pressed after the pressure drops to a safe level. Then you may need to press the alarm reset on the controller as well.
After reset, keep an eye on the chiller's pressure readings if available. The condenser should expel warm (not searing hot) air when working correctly. The fans should run smoothly, and the pressure should remain within normal operating range.
Dealing with refrigerant pressure is sensitive. Technicians have the expertise to safely handle high-pressure refrigerant problems and restore the system without risking equipment damage or personal injury.
