Overview #
On Dometic Marine Chiller HVAC Systems, an HPF code indicates a High Pressure Fault.
A high-pressure fault is typically related to a reduction or loss of proper water flow through the HVAC cooling circuit. The system monitors operating pressures and temperatures as a protective measure to prevent damage to the condensing unit and associated components.
The HPF alarm should be treated as a protection shutdown and investigated before returning the system to normal operation.
What Causes an HPF Fault? #
Mechanically, the HPF code indicates the activation of a High Limit Switch.
This temperature safety switch protects the system by shutting down the condensing unit when the circulation water temperature reaches approximately:
120°F (49°C)
This prevents excessive water temperatures that could damage:
- Piping.
- HVAC components.
- Condensing equipment.
- Circulation system components.
Common Causes of HPF Faults #
A high-pressure fault may occur due to:
Loss of Seawater Flow (Cooling Mode) #
Possible causes:
- Closed seawater seacock.
- Restricted sea strainer.
- Air entering the seawater system.
- Faulty seawater pump.
- Blocked intake.
Loss of Circulated Water Flow (Heating Mode) #
Possible causes:
- Restricted circulation piping.
- Air trapped in the system.
- Pump malfunction.
- Reduced water circulation.
Fouled Condenser Coils #
Contaminated condenser coils reduce the system’s ability to transfer heat.
Coil fouling occurs when contaminants accumulate on heat transfer surfaces, increasing thermal resistance and reducing HVAC efficiency.
Common causes include:
- Marine growth.
- Scale buildup.
- Debris.
- Contaminated seawater systems.
Importance of Seawater Temperature #
Seawater temperature has a direct impact on marine HVAC performance.
During cooling operation:
- Systems operate most efficiently in seawater temperatures below approximately 90°F (32°C).
- Higher seawater temperatures reduce system capacity.
- High-pressure shutdowns may occur when seawater temperatures exceed approximately 85°F (29°C) depending on system load and conditions.
During periods of elevated seawater temperature, reduced cooling performance may be normal; however, repeated HPF alarms require investigation.
HPF Troubleshooting Procedure #
Before requesting service, inspect the following areas:
1. Verify Seacock Position #
Confirm:
- Seawater intake seacock is fully open.
- Intake valve is operating correctly.
- No restrictions exist at the thru-hull fitting.
2. Inspect Sea Strainer #
Check the seawater strainer for:
- Marine growth.
- Debris.
- Sediment.
- Restricted flow.
Clean the strainer as required.
A restricted strainer is one of the most common causes of reduced HVAC water flow.
3. Verify Air Handler Condition #
Inspect air handlers for:
- Dirty coils.
- Restricted airflow.
- Contaminant buildup.
Dirty air-side coils reduce heat transfer efficiency and can increase system operating pressures.
4. Check for Air in the Water Circuit #
Air trapped in the seawater system can prevent proper pump operation.
Recommended actions:
- Inspect plumbing connections.
- Confirm pump is fully primed.
- Backflush the system if necessary to remove trapped air or debris.
5. Descale the System #
Over time, mineral deposits can accumulate inside HVAC seawater circuits.
If flow restrictions remain:
- Perform system descaling using an approved non-corrosive marine HVAC descaler.
- Follow manufacturer recommendations.
Technical Tip – Seawater Pump Protection #
The seawater pump includes a thermal protection switch.
If the pump motor overheats due to inadequate cooling water flow:
- The pump may shut down.
- The HVAC controller may display an HPF alarm.
The pump motor relies on intake water flow for cooling. Because the cooling passage is relatively small, it can become restricted by:
- Scale.
- Marine growth.
- Debris.
Reduced cooling flow can cause pump overheating and trigger the HPF protection circuit.
Preventative Maintenance Recommendations #
To reduce HPF alarms:
- Inspect and clean seawater strainers regularly.
- Verify seawater flow before peak cooling seasons.
- Maintain clean condenser coils.
- Inspect circulation pumps.
- Perform periodic HVAC seawater circuit maintenance.
- Monitor operating conditions during high seawater temperatures.
Owner Tip #
An HPF alarm is usually a water flow or heat transfer issue, not an indication that the compressor itself has failed. Start troubleshooting with the seawater system—confirming intake flow, clean strainers, proper pump operation, and clean heat exchangers will resolve many HPF conditions.
This guide is intended as a supplemental Ocean Alexander reference and does not replace the official Dometic HVAC service documentation.
