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What Causes High RPM When the AC is On?

1 Answers
McAshlyn
07/29/25 5:40pm
High RPM when the AC is on can be caused by the following reasons: 1. Engine control logic error, unable to receive the AC activation signal: When the system cannot determine whether the AC is on, the Engine Control Unit (ECU) mistakenly interprets it as a temporary high load and attempts to compensate for idle resistance by increasing RPM. When the engine RPM drops, it cannot handle the load from the AC compressor, causing it to increase RPM again. This back-and-forth results in unstable idle. 2. AC control circuit error, unable to send the AC activation signal: Similar to the first point, since the system cannot determine the AC's status, the ECU continuously adjusts the idle RPM, leading to unstable idle. 3. AC circuit malfunction, causing intermittent AC operation: When the AC is off, the AC compressor belt runs without load, so it does not affect the engine load. However, intermittent operation of the AC compressor forces the engine to continuously adjust idle RPM, resulting in unstable idle.
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