What Causes a Noticeable Voltage Drop When the Car Air Conditioner is Turned On?

[RubyFitz]

Turning on the air conditioner adds two electrical loads—the compressor and the high-speed fan—which can cause a slight voltage drop, a phenomenon that is generally normal. When starting the car, if the battery voltage does not drop below 9.5 volts (or 19 volts for some systems), the battery is functioning correctly, though it's best to maintain a voltage above 9.5 volts. Additional Information: While the air conditioner's power consumption may not seem high overall, during low-speed driving and startup phases, it accounts for a significant proportion of the power draw, making it easy to notice a noticeable drop in performance. However, at medium to high speeds, this effect becomes less apparent. The larger the engine's reserve power, the less noticeable the impact of the air conditioner. Conversely, in smaller-displacement engines, the effect of the air conditioner is more easily felt.