[lust4speed]

The original system on my factory air '67 red GTO was a vacuum pot that was spring loaded and increased idle as vacuum fell off. I never found the sweat spot and it always screwed up the idle with a roller coaster effect of cycling the RPM up and down. Definitely worse than not having it at all. Don't know if it carried over to '68?

[PunchT37]

Originally Posted by lust4speed

The original system on my factory air '67 red GTO was a vacuum pot that was spring loaded and increased idle as vacuum fell off. I never found the sweat spot and it always screwed up the idle with a roller coaster effect of cycling the RPM up and down. Definitely worse than not having it at all. Don't know if it carried over to '68?

I worked on a `70 Buick 455 with one of those.

[Verdoro 68]

Originally Posted by lust4speed

The original system on my factory air '67 red GTO was a vacuum pot that was spring loaded and increased idle as vacuum fell off. I never found the sweat spot and it always screwed up the idle with a roller coaster effect of cycling the RPM up and down. Definitely worse than not having it at all. Don't know if it carried over to '68?

I don't believe '68s have that.

So this was all much easier than I expected. It just took a short length of wire with a spade connector on one side to slot into the compressor circuit and a female connector on the other side to attach to the solenoid.

Default idle is back to 750. When I turn the compressor on, the solenoid kicks in. I think my solenoid is a little weak because I have to bump the throttle a tiny bit for the idle to adjust. Sounds similar to what Mick was saying. I have it at 850 with the compressor on. When I turn the compressor off idle goes back down by itself thanks to the throttle return spring.

I'll drive it around town for a bit and see how it works with the compressor cycling, but this is already way better than just setting the idle super high

[dataway]

Wonder if it's possible to add a small spring to the plunger end to give it a bit of help to lift the throttle, but no so much that it holds the high idle with the compressor off.

So you wired it to the wire that activates the clutch?

[Trevor78]

Adjust correctly.

[grivera]

Can you post a pic and part number?

[Skip Fix]

Got a funny story for you all about A/C solenoids. Built a mild 400 in the 81 TA for my kids to drive to high school . First my son then daughter. GAve up on a Holley had a 73 Qjet tuned good with a wide band. Set the A/C solenoid. Well it must have been a little stuck the first month as one day my son was driving it with his best friend and the idle kicked up to 2200! So with 3.08s it was clicking along pretty good speed! He called me freaked saying the car had a mind of its own Adjusted it and it did fine after that. He never got used to letting it warm up a little on the choke in cold weather either. Daughter never had any issues. My son still tells that story almost 20 years later!

[Verdoro 68]

Originally Posted by dataway

So you wired it to the wire that activates the clutch?

Yes, I just tapped into the connector at the clutch with a spade and ran the wire to the solenoid. It's a stock solenoid and bracket for anyone curious. I don't love running wires across the intake like this because it looks messy, but I couldn't really think of a better way.

[tjs72lemans]

When you speak of new after market units, they don't have this issue. They take less HP (about 5 to run the compressor). The old units take about 15 HP, so it's more noticeable drag on idle. My factory AC I switched to Classic Air and I see no noticeable drag that drops my rpm.

[bhill86]

I also have a classic auto air setup but I do have a drop in RPM significant enough that I installed a solenoid. I wonder what the difference is.

[lust4speed]

You might not but the rest of us do. Might be less of a load but still a load and still an RPM drop when the compressor kicks on.

[PunchT37]

Yep. My 463 has about 600 to 620 hp. It`s got a Sanden compressor. Amazing how much load it still puts on that engine. The big cam and lower vacuum don`t help either.

[bhill86]

Originally Posted by PunchT37

Yep. My 463 has about 600 to 620 hp. It`s got a Sanden compressor. Amazing how much load it still puts on that engine. The big cam and lower vacuum don`t help either.

After I thought about it I started to wonder if cam would have a significant difference as to how much load the engine would take at idle. I imagine it would. Smaller cam that provides stronger vacuum can probably tolerate a compressor better.

[dataway]

V-68 ... engine looks great.

At the current price for OEM solenoids that nice you could have paid for a whole modern AC system

I'm still totally undecided whether to restore the whole OEM AC system I still have (already a new condenser and drier) and use R12, or go with a modern replacement system. My #1 requirement is that it works well. My number 1.01 requirement is that it looks stock ... despite the fact that I absolutely despise that giant, heavy, in the way compressor.

[Sirrotica]

I'm old enough to have worked on these cars when they were nearly new, the assumption that factory cams better tolerate the load at idle is correct.

When I tuned up these cars, and set the idle, you acctivated the A/C, and put it in gear, before adjusting the idle mixture screws. I always laid my hand on the engine as I was adjusting the mixture screws to achieve the smoothest possible idle. You can achieve a very smooth idle, A/C on and in gear, with an OEM factory cam, but it takes time to get it just right. It sometimes requires decarbonizing the engine to balance the cylinders better. Any loss of cylinder pressure at idle due to sticky rings, or a carboned up valve will be very noticable at idle with the engine loaded.

At that time running a larger cam with A/C, and an automatic transmission was rare, not sure I ever remember setting up a car with both options, and a good sized cam.

Without an IAC (idlle air control) pintle, such as a fuel injected car has, getting the idle to coincide with the compressor cycling is a tough task. Maximizing the idle mixture screws under load will help, but it's not going to be perfect as a FI engine will be.

Wth a cycling A/C compressor that throws amnother variable that the older systems didn't have, the A/C was pumping constantly, and the idle speed didn't flare when it disengaged.