Idle step up solenoid bracket for Q-Jet

[cyber104]

Hi All:

After an exhaustive online search I still cannot come up with a bracket to hold a small solenoid to boost my idle when the AC is on.

This solenoid and bracket may also have been used in "reverse" (to drop the idle off when the ignition was switched off) to prevent engine "run on"

I run the original R12 system with an A6 compressor which pulls the idle down almost 300 RPM when it's running.

Thanks - any thoughts or sources would be most welcome

[firebirdparts]

They ought to be common as dirt used.  Practically everything was air conditioned.  Is this a more-or-less original configuration?  What's the original carb application?

I would have one, I think, for a late 70's 400.

[cyber104]

Completely stock setup - both AC and  Q-jet are original to the car which is a 1978 with Pontiac 400.

If you have something that would work I would be very grateful - I just can't seem to find anything

Thanks much
Chris

[pancho400cid]

Not sure what year etc. your car is.

Below is a picture of the carb/bracket/solenoid for my 78 Trans Am with L78 400.  I think this is the bracket & solenoid we are talking about?

[tajoe]

Panch shows a good picture. Is that the bracket you're looking for? Does it have-ta be exactly that? I have years of Q-jet scrounge, and probably also  have some brackets. Try and find a picture of the exact one, and I'll bet one of us has one.

[firebirdparts]

77 is the same based on what I see here in the shop.

[Wallington]

This solenoid and bracket may also have been used in "reverse" (to drop the idle off when the ignition was switched off) to prevent engine "run on"

That's how most of these operated on Quadrajets on Australian delivered V8's. Strangely enough in a hot country, the 70-90's era barely featured aircon, unlike the US. And these solenoids were set to idle speed with power on, and dropped out when key ignition turned off, effectively stalling the car. This prevented run-on or dieseling, ironically, another feature of a hot engine in a hot country, that said no to aircon but yes to annoying engine symptoms after a long trip.

Like others have said, even if you just come up with the bracket, you can often adapt different solenoids to suit. Likewise, half the guys with aircon disconnected or removed possibly still have it installed without a use.

[cyber104]

Well I did manage to source 2 different solenoid/bracket assemblies.  The one is similar to the one shown in the picture above.  The interesting thing is that this solenoid does not have enough power to "idle up" the engine.  I believe it is more suited to "drop out".  The reason I say this is that if you energize it - it is not strong enough to push the throttle linkage.  However, if you push the throttle linkage forward manually a bit - the solenoid is able to "click" and once it is locked fully extended it has plenty of holding power.

My thinking is that the one I have is designed to hold the idle until the ignition is shut off - and it is initially "set" by turning on the key and pumping the gas pedal (like we all do before starting with a Q-Jet).

I have also demonstrated this on my workbench using a 12V source.  Initially I can easily keep the plunger depressed with my thumb.  Remove my thumb and the plunger extends fully and clicks/locks into place.  Once it is in that position and energized I cannot press it back in.

I suppose I could use this type of solenoid with my AC.  But my plan was to have it energize only when the compressor is running.  If I go with this solenoid, if the compressor kicks off, the plunger will retract and not have enough power to raise the idle when the compressor comes back on - unless I blip the throttle to allow the plunger to extend and lock again.

Panch - are you sure your solenoid is raising the idle?  Maybe it's the "drop out" feature.

I suppose it's also possible that the solenoid I have is old and weak.

[Wallington]

It won't have enough power to lift the throttle, only to maintain the set level when throttle is blipped.

[cyber104]

Yes - agreed - thx for the confirmation

[nUcLeArEnVoY]

It is true that these AC idle step-up solenoids don't have the ability to actually push the throttle lever under their own power (though interestingly, they can move it a fair bit if you disconnect the AC compressor so they they get more amperage). That is by their design, so that the car doesn't start moving at a stop light.

Even the service manual and your emissions decal states that you need to rev up the motor and lift the throttle lever to make sure the plunger is fully extended before you adjust it.

The whole idea is that once you turn on the AC, you blip the throttle so that the plunger fully extends and then holds the throttle lever at the higher speed. The tradeoff is, while you will have a stable, normal idle speed while the compressor is running (as is the purpose of the solenoid), when it is not engaged, you'll have to deal with a higher idle until you turn the AC off. The solenoid plunger doesn't extend and retract in conjunction with the AC compressor cycling on and off like it would in an ideal world; it instead stays energized until you shut off the AC.

Things like this really do make you have a newfound appreciation for an idle air control valve. It's why in the future when I get a stroker motor build, I'm converting to EFI. When you're a millennial like me, it's tough to adjust to seeing your idle drop 25 or so RPM just by turning on the headlights. Lol

[Wallington]

That still happens with newer cars, unrelated to how the fuel system operates. Some may be more refined in their compensation of the new power use.

[cyber104]

It is true that these AC idle step-up solenoids don't have the ability to actually push the throttle lever under their own power (though interestingly, they can move it a fair bit if you disconnect the AC compressor so they they get more amperage). That is by their design, so that the car doesn't start moving at a stop light.

Even the service manual and your emissions decal states that you need to rev up the motor and lift the throttle lever to make sure the plunger is fully extended before you adjust it.

The whole idea is that once you turn on the AC, you blip the throttle so that the plunger fully extends and then holds the throttle lever at the higher speed. The tradeoff is, while you will have a stable, normal idle speed while the compressor is running (as is the purpose of the solenoid), when it is not engaged, you'll have to deal with a higher idle until you turn the AC off. The solenoid plunger doesn't extend and retract in conjunction with the AC compressor cycling on and off like it would in an ideal world; it instead stays energized until you shut off the AC.

Things like this really do make you have a newfound appreciation for an idle air control valve. It's why in the future when I get a stroker motor build, I'm converting to EFI. When you're a millennial like me, it's tough to adjust to seeing your idle drop 25 or so RPM just by turning on the headlights. Lol

Very good explanation - thank you!  I've got a set of 1.5" manual gauges mounted to the bottom of my dash near the E-Brake pedal.  I think I'm just going to put a small toggle switch in with them and run the solenoid from that using the "IGN ACC" spade terminal in the fuse box.  Initially I was going to tie in to the power feed at the low pressure switch - but I'm thinking for now I'll just leave the factory wiring alone and run my own circuit.  May look a little tacky but it will work and it will give me the ability to control when that solenoid is raising the idle - and when I don't want it to.

Thx everyone for the info

[Wallington]

It only adjusts the idle when you turn the AC on to compensate for the extra load and prevent stalling. I'm at a loss as to why you would want that changed to a manual switch. Or you'd simply adjust the end by winding it in so it doesn't do anything when powered up. But there's no reason for that either.

[nUcLeArEnVoY]

It only adjusts the idle when you turn the AC on to compensate for the extra load and prevent stalling. I'm at a loss as to why you would want that changed to a manual switch. Or you'd simply adjust the end by winding it in so it doesn't do anything when powered up. But there's no reason for that either.

I think he's just trying to avoid dealing with the higher idle for when the AC compressor is not engaged... sadly that's just the way things were at the time. I think the solenoid idle setting on an L78 motor with a manual trans is 800 RPM, if I remember correctly. That's what it is for my '79 W72, while the normal idle speed is 700 RPM, which is what the solenoid should theoretically keep the idle at when the compressor is engaged. Having the car idling at 800 when the compressor isn't cycled on isn't really that big a deal to me.  Automatics idle higher in park, lol.

[cyber104]

It only adjusts the idle when you turn the AC on to compensate for the extra load and prevent stalling. I'm at a loss as to why you would want that changed to a manual switch. Or you'd simply adjust the end by winding it in so it doesn't do anything when powered up. But there's no reason for that either.

I think he's just trying to avoid dealing with the higher idle for when the AC compressor is not engaged... sadly that's just the way things were at the time. I think the solenoid idle setting on an L78 motor with a manual trans is 800 RPM, if I remember correctly. That's what it is for my '79 W72, while the normal idle speed is 700 RPM, which is what the solenoid should theoretically keep the idle at when the compressor is engaged. Having the car idling at 800 when the compressor isn't cycled on isn't really that big a deal to me.  Automatics idle higher in park, lol.

Yes - you both have good points and I understand where you're coming from and this is a W72 4-Speed car so forget the "automatic" references.  But the reality is this...............

Normally my idle is about 800 RPM.  The A6 compressor drops that by about 300 RPM when it's running.  That means my idle sits at 500 RPM in 95 degree NC heat at stop lights and my oil pressure is about 10 PSI - which I'm not comfortable with.

I run NASCAR spec mechanical gauges as a redundancy to the GM electrical gauges - most folks would be perfectly happy using the GM electrical gauge to assess oil pressure and see 40 PSI at 500 RPM - but I can tell you those gauges are very optimistic and certainly not accurate - if you see 40 PSI at 500 RPM on the GM gauge - I'm telling you it's probably more like 10 to 15 in reality.

So if you connect the solenoid to a switched source - like the compressor switch for example - you will have to occasionally blip the throttle to rein-gauge the high idle whenever the compressor shuts off since the solenoid is either on or off and does not have enough power to boost the idle like a servo would - that's a pain - especially at a stop light - and even properly charged the compressor cycles quite often

Using my manual switch method - all you need to do is flip the switch when you turn on the AC - then the solenoid is constantly energized - meaning when the compressor is on I'm at about 1100 RPM with 20 PSI of oil pressure - then if the compressor shuts off I'm at about 1400 RPM and ready for the next compressor cycle on.

If you flip the switch off - I'm back to base idle.

I agree it certainly seems like a primitive solution - and if someone has a better suggestion - please bring it on - but my current approach works - good oil pressure at a reasonable RPM and good cooling.

I certainly could have tied into the feed to the low pressure switch from the original GM switch in the climate control slider - that would have given me a constant "on" also - but I would have had to tapped into the factory wiring and I would not have had the option of shutting the solenoid off when I'm running down the highway at speed.

Those are my thoughts - you can agree or disagree but it works

[b_hill_86]

I certainly could have tied into the feed to the low pressure switch from the original GM switch in the climate control slider - that would have given me a constant "on" also - but I would have had to tapped into the factory wiring and I would not have had the option of shutting the solenoid off when I'm running down the highway at speed.

Those are my thoughts - you can agree or disagree but it works

I maybe wrong, my 77 is missing all of the factory AC parts under the hood, and I’m not sure what year your car is but mine is wired the way you describe from the “constant” feed side of the low pressure switch wiring so that any time the slider is in an AC position it would power the solenoid not cycle with the compressor.

[cyber104]

I maybe wrong, my 77 is missing all of the factory AC parts under the hood, and I’m not sure what year your car is but mine is wired the way you describe from the “constant” feed side of the low pressure switch wiring so that any time the slider is in an AC position it would power the solenoid not cycle with the compressor.

That's good info - thank you.  I am considering doing that as a more permanent solution in the future.  For now I'll just use the switch until I'm sure I'm happy with the result.  Then maybe I'll tap into the factory harness - I just didn't want to do that quite yet.

[Savage Larry]

My 1977 Pontiac 400 with 4-speed didn't have the solenoid but it does have the wire in the harness. I have a 1978 carb from a 400 auto that does have the solenoid. Both cars have A/C. Are the manual transmission cars supposed to have this solenoid or only automatics?