High Pressure Switch Activates in COOL Mode

Only a lack of cooling water will activate the high pressure switch when the air conditioner is operated in the COOL mode.   The high pressure reset switch is connected to the refrigerant line leading from the air conditioners compressor.  The activation of this switch is indicative of lack of water flow.  This is the ONLY thing to cause the reset button to "trip."  Should this device activate, it is important to check the flow of water through the unit. 

Start with the sea water pump to ensure it did not lose prime.  Check for kinked water hoses or blocked lines including the sea water strainer.

Lastly, ensure the air conditioners water coil is not full of debris.  Even the cleanest of strainers can still allow silt, sand, or other debris to accumulate in the air conditioners condensing coil.  This will inhibit heat transfer and cause the air conditioner to lose cooling capacity and run warmer - eventually causing the pressures to exceed the high pressure reset button setting of 375psi.   A fresh water coil flush may be necessary, if it is deemed necessary.  Simply flush the air conditioners water coil and lines with garden hose pressure water.  The pumps in the marine industry are volume pumps, not pressure pumps.  The flow of water through a garden hose is substantially higher and can flush the debris that may have accumulated inside the water coil.  It is recommended to do this procedure at least once or twice a year.  The frequency of this will depend on the caliber of water your vessel is in.