low pressure marine chiller Problems and Direct Expansion Units: Causes and Solutions
An efficient marine air conditioning system is essential for onboard comfort, but it may stop working due to a low pressure (LP) fault. This issue can affect both centralized chillers and direct expansion units (such as split and compact systems), especially those from Frigomar, Veco, Frigit, Dometic, and Thermowell.
What is the LP error and why does it occur?
The low pressure switch (LP) protects the compressor when refrigerant pressure drops too low. If the LP alarm is triggered, the compressor stops to prevent overheating or mechanical failure.
The LP fault usually indicates a lack of refrigerant, circulation issue, or air/water side malfunction.
Common causes of low pressure in marine HVAC systems
1. Refrigerant leak
- Loose or corroded fittings
- Micro-cracks in copper lines
- Leaks at Schrader valves or connections
➡️ Leaks reduce circuit pressure, triggering the LP switch.
2. Frozen or blocked evaporator
If airflow over the evaporator is poor, the refrigerant won't evaporate correctly, causing ice buildup and a pressure drop.
3. Poor ventilation in direct expansion units
In split or compact systems like Dometic, Frigomar, or Thermowell, poor ventilation hinders heat exchange at the evaporator, resulting in abnormal low pressure.
4. Maladjusted or blocked expansion valve
If the valve doesn't allow enough refrigerant into the evaporator, the low side pressure will drop significantly.
5. Clogged filter-drier
A blocked filter-drier can create pressure loss between condenser and evaporator, simulating an LP fault even if refrigerant is present.
How to fix LP error: professional diagnostics
- Leak testing with nitrogen
- Refrigerant level check and recharge
- Cleaning or replacing filters, fans, and evaporators
- Inspection of expansion valves and electronics
- Restoration of refrigerant circuit balance
Tailored service for every boat
Our technicians service systems by Frigomar, Veco, Frigit, Dometic, and Thermowell. We provide fast, efficient, and targeted repairs, directly in port or onboard.
We operate throughout Northern Sardinia and, upon request, throughout Italy and abroad.
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