I posted this riddler a few months ago concerning my 86 westy with AC.
Radiator fan seemed to come on appropriately sometimes but once overheated
on me while sitting in traffic.  I could've swore that I had heard the fan
after shutting off the engine before but sometimes I didn't hear it when I
felt I should.  I received alot of helpful posts from listmember especially
Dennis Haynes who pretty much held my hand through the troubleshooting
process.  The fan failed the low speed fan jumper test, so when I got to the
ballast I found a suspect harness connector from the fan ballast resistor,
it evidently had sustained heat damage although the resistor tested OK and
the fan passed the jumper test after cleaning the terminals of the wire
harness.  I decided to play it safe and order a new ballast.  After waiting
3 weeks for it I didn't get around to driving any "city" driving to see if
the fan came on as it should.  Well today I drove it to work and made a
quick trip to wal-mart after driving through some stop and go after work
traffic and I was happy to hear the fan when I cut the engine off in the
parking lot.  Thanks for the help.

Ryan