Is it normal for a car to have high idle speed when the air conditioner is on?
3 Answers
It is normal for the idle speed to increase when the air conditioner is on. The vacuum solenoid valve in the car's air conditioning system plays a role in increasing the throttle opening of the carburetor through the operation of the vacuum conversion valve, which is activated when the electromagnetic clutch circuit is engaged. This results in an increase in idle speed. The reasons for unstable idle speed when the air conditioner is on are as follows: 1. Engine malfunction: The engine control logic may fail to receive the signal indicating that the air conditioner is on. When the engine control unit (ECU) cannot determine whether the air conditioner is on, it may mistakenly interpret it as a temporary high load and attempt to compensate by increasing the engine speed to counteract the resistance at idle. When the engine speed decreases, it may not be able to handle the load from the air conditioner compressor, leading to another increase in speed. 2. Control circuit malfunction: The air conditioner control circuit may fail to send the signal indicating that the air conditioner is on. Since the ECU cannot determine the status of the air conditioner, it continuously adjusts the idle speed, resulting in unstable idle speed.
I've driven quite a few cars and noticed that idle speed increasing when the AC is on is very common and completely normal. When the AC compressor engages, it increases engine load, so the ECU automatically raises the idle speed to compensate and prevent stalling or vibration. Typically, the idle might increase from around 800 RPM to about 900 RPM, which demonstrates the engine's intelligent response. However, if the idle speed surges beyond 1000 RPM or fluctuates unstably, you should be cautious as it might indicate compressor failure, loose belts, or sensor issues. For daily driving, it's recommended to turn off the AC before shutting down the engine to avoid component stress. Regular checks of the AC system during summer can help extend its lifespan and ensure safety.
From a driving safety perspective, a slight increase in idle speed when using air conditioning is necessary. Otherwise, the engine load significantly increases, making it prone to stalling, especially during traffic jams or low-speed driving. After the compressor starts, the engine needs to drive it, and the computer will increase the RPM to maintain stable output. However, this normal range should stay within 900 RPM; higher values indicate system imbalance. I once experienced unstable idling, and after inspection, it was due to carbon buildup in the idle control valve. During maintenance, focus on cleaning the intake system and checking the belts to prevent issues from worsening. Safety comes first, and regular maintenance can prevent unexpected problems.
