Why does the water temperature rise when the air conditioning is turned on in a sedan?
3 Answers
Radiator and condenser need to be cleaned, poor heat dissipation after turning on the air conditioning can cause the water temperature to rise. Introduction to car air conditioning: The car air conditioning device (air conditioning device) is referred to as car air conditioning. It is used to adjust and control the temperature, humidity, air cleanliness, and air flow inside the car compartment to the optimal state, providing a comfortable riding environment. It generally includes refrigeration devices, heating devices, and ventilation devices. This combined device makes full use of the limited space inside the car, has a simple structure, and is easy to operate, making it a popular modern car air conditioning system internationally. Car air conditioning layout: Different types of air conditioning systems have different layout methods. Currently, sedans widely use integrated heating and cooling air conditioning systems. The layout form is to assemble the evaporator, heater radiator, centrifugal blower, and control mechanism together, known as the air conditioning unit assembly.
Yesterday I also encountered this issue where the coolant temperature kept rising when the AC was on. There are several common causes: First, the radiator might be clogged—cottonwood seeds and bugs can block the fins, reducing cooling efficiency, especially in summer when the AC puts extra load on the engine, making overheating more likely. Second, the coolant level might be low or degraded; if the reservoir is low or filled with poor-quality antifreeze, cooling efficiency plummets. Another critical point is whether the electric fan is working—it should spin loudly when the AC is on. If the fuse is blown or there’s a wiring issue preventing it from running, the engine bay temperature can spike dangerously. A failing water pump (leaking) or a stuck thermostat is also common—I replaced my thermostat last year. Finally, don’t overlook the AC condenser, which sits close to the radiator. If it’s too dirty and can’t dissipate heat properly, it can drag down the coolant temperature. I’d recommend checking these areas first.
I've got experience with high water temperature when the AC is on. First, check the cooling system condition. The engine is already hot, and the AC compressor adds extra load. If the coolant circulation can't keep up, the temperature naturally spikes. The electric fan is a key focus—it should run at high speed when the AC is on. If it's not spinning, it's likely a faulty relay or poor circuit contact. A poorly sealed radiator cap can also lower the coolant's boiling point, causing it to overheat easily. Also, check the temperature of the hoses—if the upper radiator hose is scalding while the lower one is cold, it means the thermostat is stuck closed, blocking coolant flow and causing overheating. If the condenser surface is clogged with oil and dirt, it reduces cooling efficiency and doubles the fan's workload. All these issues need to be checked one by one.
