<<but the high speed cooling circuit is not. Perhaps the coolant relay is broken>>
What you want to do is check the ECT sensors resistance values.
That feeds the ACC push button control unit, which in turn , trips the coil side of the aux fan relay to complete the HIGH FAN circuit..
The ECT sensor trips at 105/107 and that is high fan [ both]
This circuit is also fused on the load side of the relay , so if you don't have high fan I would check that fuse first..or the connection at the resistor [ both circuits use a common terminal
at the resistor , even though the High fan does not use resistor]
This will be the two wire side of resistor.
I would look into the ECT circuit before just jumping the resistor and expecting that to cool high eng coolant temps , as
these fans will still not come on until the high side pressure on a/c is tripped...
You definately want BOTH systems working...
I can send you the schematic...