Q: My fan keep running when ac is on

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When ac is off, my cooling fan works fine, sometime on and sometime off, and coolant temperature is optimal around 90 - 100 C. But when I turned AC on, the fan will keep running, causing my coolant temperature to drop low to around 70 -75 C and always stay there and never go above that no matter how. When I turned the AC off, then after like 1 min, the fan will also off, and coolant temperature is optimal again.

Is it normal? What may be the cause?

Thank you

My car has 41000 miles.
My car has an automatic transmission.

Seventy degrees C (160 degrees F) is too low for optimal engine efficiency and may cause oil contamination and reduced engine life. You will get lower gas mileage, too. The cause of the sub-normal temperature is the extended fan operation but the situation could be aggravated if you also have a stuck open thermostat. To obtain a diagnostic pinpointing the root cause(s), and thence the necessary repairs, the recommended service is an electrical circuit/component diagnostic. In the course of that, the mechanic will pinpoint the fault and get it repaired. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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