I also have had problems with high current draw from my '86 Westy air
conditioning fan.  After a little thought I developed a good solution
that had the added benefit of significantly improving the performance of
the air conditioning system.

I found my Westy air conditioning fan was drawing a enough current to
overheat the fan switch.  In my case, the fan switch would last about a
year before the high speed switch contacts would overheat and fail.  I
eliminated the problem with the switch by installing a gang of three 40
amp load reduction relays inside the air conditioning cabinet to provide
the current to drive the evaporator fan.  The current for the fan was
provided by the +12 VDC terminal in the wiring connection box in the
engine compartment via a heavy gauge wire and an 50 amp circuit
breaker.  The relays were controlled by the original air conditioning
fan switch, one for each speed.  All wiring connectors were crimped and
soldered.  I found the high speed relay would stick after long runs so I
piggybacked a second relay in parallel to split the current draw.  This
has worked very well with no problems for several years.

One unexpected benefit is now the air conditioning fan is supplied with
power that has not suffered the considerable voltage drop from the
original fan switch and small gauge wire.  I did not measure the voltage
available at the fan in the stock configeration but it had to me much
less than it is now.  The air conditioning now works much better because
the fan blows much stronger.  The present Low speed is about equal to
the previous Medium speed.  The High fan speed is awesome and is more
than adequate in blowing cold air up to the driver and front seat
passenger in hot weather and is actually too strong except for initial
cooling off after sitting in the sun.  In fact, I had previously
installed a second evaporator unit over the glove compartment (another
story altogether) to cool the folks in the front.  With the improved fan
operation, the second air conditioning unit would not have been
necessary.

I highly recommend adding load reduction relays to provide adequate
voltage to the air conditioning fan.