I realized I don't understand the three speeds of the
radiator fan when the temp sensor only has two outputs.

I'm looking at Bentley 97.141 for my '87 Syncro Westy
and the way I read it is:

AC off:  radiator temp sensor runs the fan at low speed
or high speed, according to the 95 C switch and the
102 C switch.  Fan never runs at middle speed.  The
low speed is via the resistor and the high speed via
the 3rd stage relay.

AC on:  fan runs at low speed, unless AC high pressure
switch closes and then it runs at middle speed.  This
via the 2nd stage relay (tracks 14 and 22)  But
when the AC clutch is running, fan always runs at
high speed.  (Tracks 17 to 18 to 20)  Is this correct?

I don't think my AC does this; if that is how it should
work, I'll have to figure out why mine doesn't.  I know
my fan runs at low speed when I turn on the AC.

Thanks,
Richard