Engine coolant is starting to overheat. Doesn't matter if the A/C is turned on or not. Normally the elect. Cooling fan runs more frequently when it is turned on. Doesn't cause temperature to rise when at highway speed. Just when idling at a long traffic signal. Radiator coolant is o.K. Coolant level in reserve tank is o.K. No visible leaks pooling under vehicle. Coolant is 50-50 strength. No leakage coming from hoses.