The A/C switch used in many Westies was installed by the US dealer and
importer.
It consists of a 3 speed fan swich and a thermostat ring.
With age the switch part burns up as the fan takes a lot of current.
Mine burnt up and I have seen other postings about the same problem.

This switch is very hard to find new, however something similar is quite easy
to find, at least in USA.

I have found a switch at NAPA that is the same manufacturer, "INDAK" and has
the same fan switching section but no thermostat adjustment ring.
This switch can be taken apart and the parts used to replace the burnt up fan
switch parts in your old one.  A pressed copper switch plate and a paxolin
plate holding the 5 spade connectors are the parts you need to exchange.
Keep the dialectric grease on the new parts.
Its necessary to bend some metal tabs back and fight a small spring, but any
"handyman" can do it.  The shaft inside is so shaped that you cant put
anything in the wrong way round.

The NAPA part number is 207419 and it costs $12 .

I have been using this fix in my '84 Westy for about 6 weeks now and
thankfully my A/C has been working well.
This fix got me out of trouble and I hope it will for others too.

Cheers,
Steve Cotsford
Columbia SC.....hot hot Hot !!