it seems like it never does...

 

I have asked that question to one of the tech at Mitsu. He said that it only activates via the fan. He said that when it gets hot enought and the fan turns on, the spray quirts, for what he said, a few seconds. Never seen it myself though.

 

Notice how the light only comes on when resetting back to auto mode. It would be nice if it came on when manually pressed. You just have to hope its working, or sometimes you can smell the washer fluid.

 

Seems like it ought to be based on the intake air temp but I don't really know.