97 Subaru outback overheating - fixed by turning ON AC

Every once in a while in heavy traffic the engine overheats. I can’t get out to check on the highway bit I suspect a an isn’t on. I can drop the temp in the usual way of blasting the heat but I can also drop it precipitously by turning on the AC! It seems to stay down even if I turn the AC off - at least for a while.

The radiator is new and it has plenty of fluid.

Any ideas anyone?

The reason turning on the AC will cool it is that this turns on the cooling fans. You are having a problem in the cooling fan circuit/control someplace so that the fans aren’t coming on when required to cool it down. This should not be a big deal for any mechanic to find.

I think you have a problem with the radiator fan or it’s circuitry. Turning on the AC will also turn on the AC fan which will cool down the radiator. Just check under the hood sometime with the AC off and your engine fully warmed up. The radiator fan should be running. It would be a fairly easy fix for a good independent mechanic.