Water pump: It allows the refrigerant to flow inside of the engine.
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It is inside of the engine but it is surrounded by a serrated belt. The timing belt of the engine moves it. After some time, its internal booster may get damaged and stop pumping liquid. You should replace it every time you change the timing belt.
My 2000 1500 Silverado started running when I was hauling something a few weeks ago and would cool down when I would turn it off. Then it started getting no matter what if I was hauling something or not so I changed the water pump, fan clutch, radiator, all new holes, new thermostat