WHen a/c is running car kicks fan into hi gear. What causes this
2 Answers
Your fan should run when ac is on and car is at an idle or at low speeds.
When running the A/C, there is an increased fan RPM (caused by a relay) to create more airflow through the radiator and A/C condenser. It's the airflow that leeches heat away from the A/C coolant and engine antifreeze and ensures the continued proper function of both systems.