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Solved problems · Electrical · Crew answer

Why isn't my boat's air conditioner cooling?

Most marine air-conditioning problems trace to seawater flow, dirty air filters or a power issue. Check the strainer, pump and overboard discharge first, then airflow.

Symptom

The air conditioner runs but blows warm, cycles off with a high-pressure or similar fault, frosts up on the evaporator, or won't start at all.

Likely cause

A seawater-cooled unit dumps its heat into water pumped through the condenser. A clogged strainer or intake, a failed or air-locked pump, a kinked hose or a fouled condenser stops that, so pressure rises and the unit shuts down. Inside, a dirty return-air filter or blocked duct starves the evaporator, which can ice up. A tripped breaker, low shore voltage or a loose terminal keeps it from starting.

Stop now if

A breaker trips repeatedly, wiring or the unit smells burned, or water is leaking into the boat from a hose. Turn the unit off at the breaker and get service. Turn off the AC breaker before opening the unit or touching wiring, and close the seacock before opening the strainer.

The fix, in short

  1. Check the overboard discharge. With the unit running, look for a steady stream of water from its overboard outlet. A weak or missing stream means a flow problem.

  2. Clean the strainer. Turn the unit off, close the seacock, then open and clean the strainer basket. Reopen the seacock and check the lid seals so the pump doesn't suck air.

  3. Check the pump. Make sure the seawater pump runs and is primed. Many are centrifugal pumps that won't self-prime if air gets trapped. Clear air as the maker describes.

  4. Clean or replace the air filter. Dometic points to dirty filters and blocked ducts as a common cause of weak airflow and evaporator icing.

  5. Check power. Confirm the breaker is on and shore voltage isn't low, especially at the end of a long dock. Have an electrician check loose terminals.

  6. Call a technician for refrigerant work. If water and airflow are good and it still doesn't cool, or the fault repeats, the condenser may need descaling or the refrigerant circuit may need service.

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Air conditioning: Self-contained seawater-cooled marine air conditioner, seawater pump, strainer, condenser, return-air filter and ducting

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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