92 Legacy , New to thread new to Subaru. Question: How do these radiator fans work? When car is stopped and at idle, Fans come on at various times and then the Idle speed drops or go up depending on if fans are on or not. drops to 400 rpms then up to around 8-900rpms. At idle it will do this about every couple of minutes. Any ideas?

your fans work basicly like this,when the engine gets up to temp they kick on[dont usually kick on while driving because incoming air is the same as]when temp drops to maybe 185 they shut off,when it hits 200 they kick back on. now2 if you have the air,defrost,,heat-defrost on the compresser will run maybe cycle off and on,i think this is where yours is going up and down,see how it does with heater off when car is up to temp. your fans will run if air,defrost,heat -defrost is selected on the heater control.

Correct.

 

 

One fan is controlled by the coolant sensor, the other only runs in connection with the A/C - and that will come on with the windscreen defrost.

 

The low idle is the normal one. The A/C compressor asks for the increase in idle speed.