[tjs72lemans]

Now that I got my AC functioning, I wanted to set the idle solenoid. I also noticed my idle seemed a bit high without AC and was going to back it off (wanted about 700 and had about 1000 RPM). This was set by Cliff after a rebuild. I noticed the idle solenoid was not touching carb idle set throttle bracket when car was off and cold. But once started, the solenoid bolt was touching carb bracket. As I turned AC on nothing changed. I was going to disconnect wire to solenoid and the solenoid bolt then moved. As I moved the solenoid wire, the solenoid bolt would move in and out. This was even with the AC control off. It seemed to kick in and out with control on or off. I realized my higher idle was from the solenoid being kicked out. With it fiddled with and off, my idle was down to 700. Why is this solenoid energized all the time? Where do I look to fix?

[Goatracer1]

It sounds like someone wired it as an anti-dieseling solenoid rather than an AC solenoid. First of all are you sure it is an AC idle up solenoid? If it really is then you have to change it's power source. Shouldn't be too hard to wire it to come on when the compressor clutch engages.

[tjs72lemans]

It is an idle up for the AC. I am wondering if there is a short in the wire somewhere that would allow it to function as I move the plug to it. It just seems odd it functions when AC is off. I would think no power should be going to it until the selector levers are moved to AC, etc.

[Skip Fix]

Should bump up as the compressor is engaged.

["QUICK-SILVER"]

72 had a hot wire under the hood that cut on and off with the ignition switch. It was for smog timing control and easily got mixed up with AC wires.

Clay

[padgett]

You mean the TCS switch ?

["QUICK-SILVER"]

Originally Posted by padgett

You mean the TCS switch ?

It powered up the TCS harness. Which went to several switches Like temperature switch/sender, on/off vacuum solenoid, transmission switch, etc..

Pretty sure wire colors for that mess was the same used with AC wiring. Connectors fitting and wire colors being right was how things got mixed up.

Clay

[tjs72lemans]

I have the TCS wires unhooked (recommended by another member here) and laying by the TCS switch. The idle up solenoid wire is yellow with a black stripe and has the rubber boot to connect to the solenoid. Would not having the TCS switch wired in place cause any issue with this solenoid wire getting power all the time?

["QUICK-SILVER"]

Looking at 72 Firebird non AC wiring diagram, that yellow/black is hot with key ON and does power idle-up solenoid. Idle-up is the same thing as anti-diesel.

With key ON idle-up.. Car may not be suppose to have AC throttle bump.

If you don't need or don't want to use idle-up.. Leave yellow/black unplugged and run a jumper from AC clutch power to the idle-up solenoid.

Clay

[tjs72lemans]

Why would a non AC car have the idle up solenoid? I thought this was just powered when the AC was kicked on to bring the rpm up to compensate for the compressor draw?
I bought this car in parts and restrung the original wiring harness as I followed the manual wiring best I could. The natural bends in the pre existing routing and terminal ends helped me.
If all else fails, I'll abandon trying to run that portion of the original wiring and wire my own from the AC on wiring.

[Kenth]

Originally Posted by tjs72lemans

Why would a non AC car have the idle up solenoid?

Many 1968 and later vehicles with retarded timing/ported/timed source for the vacuum advance uses an anti-dieseling solenoid for curb idle settings.

[tjs72lemans]

I read the service manual last night on this and became well informed of it's function. I was initially told a while back on here the function of that solenoid was to bump up the rpm when the AC load came on. Now I see the idle stop solenoid, as it's actual name, is for anti dieseling. It looks like it's meant to keep idle at 200 rpm higher than when engine is shut down. On shut down it retracts off accelerator arm to allow less rpm and ant diesel. I'm not sure I even need this hooked up after all if I don't experience a run on issue. The AC does drop rpm down, but not sure it's enough to affect normal engine operation.