Marine air conditioner pumps fail for a number of reasons, low or no water flow to the pump. Clogged line to the air conditioner, pump is not located properly in the boat, it has to be below the water line. The pump is sized to small for the application. Using a water hose connected to the output hose of the pump make sure there is an adequate flow from the discharge line of the air conditioner. If not clean or replace the hose. Second, from the strainer with the boat in the water and the hose disconnected to the pump make sure when the through hull valve is open there is a water flow, if not lower the strainer until water is flowing from it. The MPS pumps come with a 120 VAC plug for testing purposes. Don't mount the pump but connect the hoses to it, then plug it into a temporary power source and test it. If water is adequately flowing from the A/C output you should be go to go. Hard wire it to your A/C using proper connectors, and mount the clamps to hold the pump in place.