Why the engine coolant temperature increases to the maximum level when you turn on the air conditioning in a 2000 grand prix gt and it decreases if you turn off?
When you switch the A/C on, the A/C compressor engages and puts an extra LOAD on the engine. The engine has to work harder to drive the A/C system. This extra load causes heat inside the engine and the coolant must carry this extra heat away. As the coolant picks up more of the heat, you will see the temp rise. Once you disengage the A/C, the coolant doesn't have this extra heat to carry so the temp goes back to normal operating temp.