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Diagnosing

Checking a Marine Air Conditioning Seawater Pump

The short answer

Look for the expected seawater discharge and note unusual pump sound or visible leakage from a safe position. Stop the air conditioner if flow is absent. Do not touch potentially hot equipment, remove covers or open a seawater line while trying to identify the cause.

Checking a Boat AC Seawater Pump — Requirements and Limitations

A centrifugal pump can run without delivering the required flow if it loses prime or the intake is restricted. Sound alone cannot distinguish an airlock, blockage or electrical fault.

After strainer service or layup, follow the exact pump priming instructions. Record what changed and ask a technician to verify flow and supply if normal discharge does not return. The pump curve, installed head and air-conditioning requirement must be considered together.

Steps for Checking a Boat AC Seawater Pump

  1. Confirm the seacock is open and the strainer is clear first — a starved pump sounds like a failing one.
  2. With the unit running, feel and listen at the pump housing.
  3. Hot and humming, no flow: crack the highest fitting on the seawater line to bleed any air.
  4. Still nothing after bleeding: the impeller or the pump has failed.
  5. Silent and cold: check the pump's own breaker or fuse before condemning it.
  6. A gravel-like noise is cavitation — a restricted intake, which is a flow problem upstream.

Each of these answers a different part of the same problem.

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