The Stovebolt Site Forums The Shop Area General Truck Talk AC idle stop solenoid installation

A recent post inquired about installing an idle stop solenoid for an A/C installation. This post gave me some motivation...

I had not installed one when I put in my A/C last summer, and the post reminded me that I should quit procratinating and get it done. I was making due by increasing the no-load idle speed. This worked, but my no-load idle speed was more than what it needed to be and my A/C idle speed was probably a bit too low to properly cycle the freon at idle.

I could not find any posts showing past installations, so I thought it might be helpful to show pix and describe how I did the installation on my '57 3600 with a 235 and a Rochester Model B carb.

The pix have descriptions of the project attached to them, but I did not show the electrical. The solenoid is wired on a 5 amp fused line that was spliced into the compressor wire. When the compressor is switched on, power goes to the solenoid. I did not run this through a relay because the draw for the solenoid is so minimal.

It works great except for one thing...the solenoid does not have enough power to adjust the throttle on its own. When the A/C is turned on, I give throttle a quick goose and then the solenoid does its magic.
Works like a charm.

I have the no-load idle set at 650 and the A/C idle set at 900. The solenoid has allowed me to individually fine tune the no-load idle and the faster A/C rate (to cycle freon at idle).

Here are the pix with installation descriptions--

http://s844.photobucket.com/user/ma...6251_zps2053e8f6.jpg.html?sort=6&o=0

Hope this helps anyone thinking about a similar project.

Maybellene

Nice mod. Have you considered moving the solenoid further out toward the end of the linkage extension rod? This might give you more mechanical advantage from additional leverage to allow the solenoid to have the power to open the throttle without your assist.
Carl

Carl, thanks. I tried it...even tried a longer screw that would let me push the solenoid out even further hoping for more torque. No luck. Thanks for the idea, Matt

Even the standard equipment selinoids would not kick it up till the throttle was cracked.

I need to design one for the edelbrock on the '56.

How do you tell when the compressor is on, as in cycling on?

The clutch is what cycles. It is on the forward side of the pulley. You can visually tell if it is spinning or sitting still.

Thanks to all for suggestions both through this forum and PM's.

Here is an update after a Saturday of tinkering. The idle stop solenoid now works automatically as I hoped that it would.

I lengthened the replacement idle screw by about another 1/2" and widened the bracket to 2 3/8". I pushed the solenoid out to the edge of the new bracket to gain more leverage with the longer idle screw.

I rewired the solenoid using an SPST relay. The relay is triggered by the compressor wire. The solenoid is still wired with a 5 amp fused line, but it now has its own feed instead of drawing directly from the compressor line.

I run the AC idle speed at 50-100 RPM over no-load idle speed...250 was too much. This seems plenty to better cycle the freon...and I no longer see a major dip on my dash ammeter when my AC is turned on as I did without the solenoid. The change in the idle speed when the AC is turned on seems much more seamless, but is enough that my ear can tell if the solenoid is working correctly.

Once the solenoid is dialed in to run 50-100 RPM over no-load idle speed, it can be left alone. Adjusting the no-load speed with the idle screw is the only adjustment necessary for the carb. Since the new, longer idle screw remains on the same plane regardless of how the idle screw is adjusted for no-load idle, the difference between AC load and no-load remains constant.

The rig works equally well when I turn the AC on or when the compressor cycles during operation.

Revised pix are on the same photobucket link listed above.

Thanks to all my 'bolter friends for helping me to refine the original design. Hopefully anyone else attempting a similar project now has a working model to start with.

Matt

Congrats, looks great.

I didn't realize the solenoid was to help the compressor. I thought that the motor needed a little more power to maintain idle with the compressor engaged. I thought maybe with an automatic, it would be essential.

The solenoid does help the engine. The help is needed due to the strain of the compressor. Here is how it works--

The compressor pulley always spins. It free spins when the compressor clutch is not engaged. When the AC is turned on, the compressor clutch engages. The pulley now does real work to operate the compressor. This pulls some power from the engine. At idle, this strain pulls the idle speed down...enough to sometimes stall the engine. The solenoid gives the engine a bit more gas to compensate.

The same thing happens when the thermostat causes the compressor to cycle. If it calls for AC, the compressor clutch is activated and the load is added to the engine. The solenoid compensates so that the engine automatically idles the way it should when the compressor clutch engages and disengages.

The solenoid only comes into play at idle. Your foot on the gas compensates when driving.

The compressor load (about 5 HP from what I have read) is always on the engine when its clutch is engaged whether idling or driving. At idle, it is very noticeable. When driving, it is less noticeable but you can tell that performance is reduced.

Remember back in the old days when people would talk about losing MPG due to air conditioning? It is because of the extra load put on the engine.

Some vehicles have a vacuum operated cut-out that automatically shuts down the compressor clutch during hard acceleration so that all power goes to the drivetrain. I did not install one in my application.

Matt

A few final notes due to some PM'S...

I listed the no-load idle speed incorrectly above. It is set at 500 RPM. (Gettin' old...read my notes wrong.)

The idle speed with the compressor engaged and the solenoid activated is set at 550.

The compressor load reduces the idle speed by 250 without help from the solenoid.

Matt

Does your Photobucket link still work? I can't seem to get the photos to load. I'm interested in seeing how you added the solenoid.

Welcome. First you have brought up a 6 year old thread. Second, Photobucket links died long ago when they started charging for their service. Please start a new thread and our currently active members will help. The OP still monitors Stovebolt so he may respond with photos he can post directly to this thread. Instructions are in the left margin of every page.

Idle stop solenoids are one of the interesting mysteries to me. In the 60s, 70s and early 80s if you paid more than $4 or $5 for one, you had just been ripped off royally. Today go out and look for a new one. $50, $60, $70...for a simple 12 volt solenoid? Really? That's just nuts. A solenoid is one of the simplest electronic devices there is and a plain push solenoid with a screw for adjustment could be made by 5th grade kids as a basic science project. What in the world happened? Just lack of demand?

I'm looking for one of these, by the way. If anyone has one (and I can convert nearly any of them to fit), please send me a PM.