I've got the same or at least a similar problem with my radiator fan.

The low-speed fan kicks in as expected but the high-speed fan never kicks
in.  But I know it works since I've done the jumper test at both the switch
and at the high-speed relay.  I have replaced the switch.

Maybe the coolant is not getting hot enough for it to kick in -- I'm in
Victoria, BC where it never really gets super hot, but I would have thought
that going up long hills at highway speed on a hot day (~85 degrees F)
should be enough to trigger the high-speed fan.

At what temp should it kick in?  I've got an infrared temp gun so I could
test that.

Thanks, Rick

On Tue, Sep 5, 2017 at 3:24 PM, Dennis Haynes <d23haynes57@hotmail.com>
wrote:

> Is the radiator getting hot? For testing the wiring there are three wires
> on the fan switch. One is power from the fuse box. That wire jumped to the
> middle will give you slow speed. The two outside wires jumped will give you
> super-fast high speed. If the fan turns on with the AC than most likely the
> fan resistor is good. It is possible you just are not getting the coolant
> hot enough to call for the fan. Infrared temp gun can help here.
>
> Dennis
>
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
> Of David Bjorkman
> Sent: Tuesday, September 5, 2017 1:24 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Radiator fan switch
>
> Hi all;
> Still in SC. replaced the radiator and condenser (after some body work)
> and am having trouble with the fan coming on. Turning on the A/C gets
> starts the fan, so I know it works, but it won't start when the engine gets
> hot.  Fuses check out OK.  How does one check the radiator fan switch.  I
> know that I have to jumper something, but not sure what.  I would really
> like to get this fixed and get back home.
>
> Thanks;
> Dave B.
>