> From:    John Bange <jbange@GMAIL.COM>
> Date:    Sun, 27 May 2007 10:33:05 -0700
>
> After the fourth or fifth time, it occurred to me that it would be
> handy if the full throttle enrichment switch would also disengage
> the AC compressor clutch.  Of course, since the Digifant full
> throttle switch does double duty as the "no throttle" switch, it
> wouldn't work to just scab onto it with a relay.

I agree with the other posters that a vacuum switch might be a good way
to go.  Sometime between 1970 and 1990, some car almost certainly had
a vacuum switch in the smog control stuff that would switch at the
vacuum level you want and handle the current drawn by the compressor
clutch.  Unfortunately, there probably is no cross-reference available
to mortals that tells you that part number 12345 (what the parts guy can
order it by) is a 5 psi 20 amp switch (what you know).

I have used a World Magnetics PSF109S series switch (see the bottom of
http://dkc3.digikey.com/PDF/T072/P2120.pdf ) in a very similar
application.  It really is adjustable like they say.  The only trouble
is that its DC rating is only about 1 A, so if you need to switch
serious juice you have to use a relay as well.  The switch costs about
$16.

A Honeywell 5000-series vacuum switch (see the bottom of
http://dkc3.digikey.com/PDF/T072/P2105.pdf ) might handle enough current
by itself to work.  These aren't adjustable, though, so you have to
guess right the first time.  These switches are about $24.

Standard disclaimers apply; I don't get money or other consideration
from any companies mentioned.

Matt Roberds