What Causes Significant Voltage Drop When Turning on the Car Air Conditioning?
2 Answers
Turning on the air conditioning adds two electrical loads—the compressor and the high-speed fan—which naturally leads to a slight voltage drop, and this is generally considered normal. When starting the car, if the battery voltage does not fall below 9.5 volts (or 19 volts for certain systems), the battery is functioning properly, though it's ideal for the voltage to remain above 9.5 volts. Additional Information: While the air conditioning system's power consumption may seem modest overall, during low-speed driving and startup phases, it accounts for a significant proportion of the electrical load, often resulting in noticeable power loss. However, at medium to high speeds, this effect becomes less pronounced. Vehicles with larger engine reserve power experience less noticeable impact from the air conditioning, whereas smaller-displacement engines are more susceptible to noticeable power reduction when the AC is in use.
Why does the voltage drop significantly when the AC is turned on? Once, I was driving out for fun and it was so hot that I turned on the AC. Suddenly, the voltage on the dashboard dropped sharply, which almost scared me to death. After asking an old friend, I realized that the alternator couldn't handle the sudden load: when the AC compressor starts, it requires a lot of power. If the alternator is an old model or the belt is loose, the power supply can't keep up. An aging battery can also cause trouble, leading to unstable voltage that affects the brightness of the headlights and even makes the engine misfire. This issue is especially noticeable during hot summer days when high temperatures in the engine bay cause components to overheat more easily. Later, I developed a habit of having the shop test the battery and alternator output during my bi-annual maintenance. Preventive checks can save a lot of trouble. Safe driving is crucial—don't wait until you're stranded on the road to regret it.
