Chilling thoughts

[jbcollier]

As you all know, I fitted AC to my S1.  In general I’m very pleased but there are a few details still to sort.  The first is some way of increasing the idle speed when the AC is used.

My first thought was to fit an idle-up solenoid made for the job for US cars.  Unfortunately the solenoid is not powerful enough to push the throttle open.  It will work if the throttle is already open but not open a closed throttle.

My next step was to use a larger solenoid with separate pull-in and hold-in windings.  This gives a big shove to open the throttle but then settles into a low current draw to hold it open.  Clever but necessarily larger which means it had to be remote mounted and work through a cable.  I hooked it all up and adjusted it.  Bingo!  It works.  Flip on the AC at idle and it jumps up to 1200 and works perfectly.

Excellent... until I blipped the throttle.  It went up to 3000 rpm.  Great for cooling I suppose but not otherwise.  The solenoid cable was acting like a spring and pulling just a wee bit more when not under tension.

The problem is that you are working 4 large butterflies so very small movements make a huge difference.  I now understand why Afla used a hand throttle on their cars.  I’ll have one more go with a solid wire cable.  If that still doesn’t work then I’ll go the Alfa way using an aircraft control cable.

[surfguitar58]

Just a thought... Using a solenoid to do actual work is often a big current draw. What about using some sort of vacuum actuator to do the actual heavy-lifting throttle work controlled by a low-current solenoid valve?

t

[jbcollier]

That why you use a solenoid with two windings.  The pull-in winding draws 15 amps but the hold-in winding draws less than 1 amp.  As the solenoid nears full travel, it opens a set of points that cut off the pull-in windings.  It all works exactly like the solenoid on a starter.

[dakazman]

  Does the speed come down if the ac is shut off? After blipping? Can we do a rpm powered actuated ac solenoid on only below 1200?  Just spitballing.
Dakazman

[surfguitar58]

That why you use a solenoid with two windings.  The pull-in winding draws 15 amps but the hold-in winding draws less than 1 amp.  As the solenoid nears full travel, it opens a set of points that cut off the pull-in windings.  It all works exactly like the solenoid on a starter.

That makes sense. What dual winding solenoid are you using?
t

[jbcollier]

Something off a Kubota lawn tractor.  Not sure what its original purpose was.

When the AC compressor cycles off, the idle-up solenoid powers off and all returns to normal.

[dakazman]

Something off a Kubota lawn tractor.  Not sure what its original purpose was.

When the AC compressor cycles off, the idle-up solenoid powers off and all returns to normal.

Yes John, I was thinking about a adjustable low oil pressure switch to supply power to solenoid  , however I don’t know how much pressure you lose at idle at those speeds.
Dakazman

[shootingsight]

Is there an air bleed inlet that is upstream of the jets?  You could get a solenoid valve that opens a circuit the bypasses the butterflies.  Or is it butterflys?

[jbcollier]

There is a manifold vacuum port that could be used that way.  Unfortunately you would also lean the mixture.  This is where EFI shines.  Adding a little more air is no big deal and the system adds fuel to make it all work.

[Lotuswins]

Hi John,

I am working on the same issue with my Healey 3000 A/C installation.  I think I have a resolution though, and it involves having a solenoid actuate the SU HS6 choke cam, rather than the throttle linkage.  You can move the choke cam independently for part of its travel before it engages the needle seat dropping lever which enriches the mixture.   Only one carb need be addressed, just to up the idle a tad......been waffling on it though since keeping the idle high (1k) seems to mitigate it in the summer.....so no real incentive since I drive the car rarely. 

If you have EFI? then perhaps a longer lever arm or cam is needed?  The US solenoids do have a rather large travel......that would reduce the force needed to open the throttle....but you probably have thought of that one.....

jerry rude
4005R

[jbcollier]

With some EFI systems the IAC takes care of it.

(idle air control)