1957 A/C Idle Speed Up

[james wagnon]

Hello, Can anyone tell me how the idle speed up device on a 1957 works. It is partly vaccume and partly electronicly operated but I am unsure of the theory of operation. Also where do the 2 wires that come out of the front of the device and disappear into the wiring harness then traverse through the firewall, connect under the dash? Is it to the some of the prongs on the A/C switch? If so what color goes to what prong? Thanks in advance, James Wagnon

[DaveW]

James,

Do you have the 1957 Shop Manual?  If so, check out pages 10-1 and 13-4.  I am surely not an expert, but will summarize what I know based on the operation of the fast idle switch on my '58 and the information in the '57 manual.  Hopefully someone will chip in to correct any errors I make in my explanation.

The fast idle solenoid is only active when the car is in neutral or park and the A/C is on.  The vacuum supplied to the switch normally holds the plunger back.  When the solenoid in the switch is electrically energized the plunger pushes on the lever connected to the throttle blades increasing the idle speed.  In addition, if the choke is on, the choke modifier rod should slightly open the choke.  Once the shifter is placed in gear the solenoid is electrically deactivated and the vacuum pulls the plunger back.

The circuit diagram on page 13-4 shows a black and a violet wire coming out of the fast idle solenoid.  The black wire goes to a junction where one leg leads to the compressor clutch solenoid and the other leg goes to the compressor switch.  The violet wire goes to a junction where one leg goes to the neutral switch and the other leg goes to the ignition switch.

Hope this helps,
Dave

[J. Wagnon]

Dave, Thanks for the lead. My idle speed up unit does have one black and one violet wire coming from it. These wires disappear into the black taped wiring harness that goes thru the firewall and re-appears under the dash in the area under the radio. I belive there are 2 violet wires and one green wire that come out of the taped wrapped harness at that point but I am unsure where to connect them. The vacuum side of the unit does indeed hold the plunger back from the throttle blades and is functioning properly. It is my belief that the electrical side of the unit, when power is applied, should cause the vacuum to break thereby releasing the plunger to engage the throttle and speed up the idle. Is this correct? I have taken out the 2 screws that hold the coil in the unit housing. I then tested the coil and the 2 wires coming from it to see if I had connectivity. That is, could I complete a circuit thru the coil and wires. I could, so in my mind the unit should work. Right? But I can not see or don't understand how it works. I can see no movement when power is applied to the coil thru the wires. Should it move? Is it designed to extend slightly thereby creating or breaking a seal over a small hole in the housing? If this is correct should there be a neo-pream O ring between the coil and the housing where the small hole is? I do not have an O ring or any type of gasket in this area, but I also do not see any movement on the part of the coil. I guess I need help understanding the theory of operation as it pertains to the electrical side of the device as well as suggestions on how to  test my unit. Perhaps there is a carburetor expert out there who rebuilds these units? Any thoughts would be appreciated. James Wagnon

[J. Gomez]

James,

The electrical portion of this solenoid is to activate (power on) or deactivate (power off) a small plunger inside the unit (small spring pressure returning plunger to normal w/power off) and thus opening or closing the vacuum path.

The large plunger that extends to the carb works with vacuum. There are no “O” rings inside the unit just only a rubber diaphragm inside the vacuum canister.

For you see if the plunger works you will need vacuum to be apply to the unit, while turning power 12v on and off to the solenoid.

I’ve added the missing pieces to the electrical wiring (attached) from my 1956 manual showing the idle speed up control which was MIA from the manual. The 1957 should be similar.

HTH

Good luck..!

[J. Wagnon]

Jose, I have no plunger inside the electrical side of my unit. When I remove the 2 screws that hold the coil inside the housing the coil, wires, and fiberboard end cap that the coil is attached to come out of the housing. The coil is attached to the fiberboard by either a brad or an odd shaped phillips head screw. This brad? appears to go all the way thru the coil and the other end is hollow. The hollow end lines up with a small pin hole in the housing that relieves the vacuum. Should there be a plunger in here somewhere? Thanks, James Wagnon

[J. Gomez]

Jose, I have no plunger inside the electrical side of my unit. When I remove the 2 screws that hold the coil inside the housing the coil, wires, and fiberboard end cap that the coil is attached to come out of the housing. The coil is attached to the fiberboard by either a brad or an odd shaped phillips head screw. This brad? appears to go all the way thru the coil and the other end is hollow. The hollow end lines up with a small pin hole in the housing that relieves the vacuum. Should there be a plunger in here somewhere? Thanks, James Wagnon

James,

The link below shows the MPL page for the idle speed up control internal components. The Carter and Rochester carbs are different but they function the same.
It seems you may be missing the small plunger and the spring for the solenoid to open and close the vacuum passages. 

http://www.modifiedcadillac.org/documents/Shop_Manuals_and_Illus_Catalogs/Master%20Parts%20List%20thru%201964/Group%203/tn/Group%203%20-%209.jpg.html

Good luck..!

[J. Wagnon]

Great! Thank you so much. James Wagnon

[J. Wagnon]

Thanks for the great info. I can tell from looking at the picture for the rochester unit that I am missing 2 internal parts. One is the spring (N.L.- Spring) and the other is the Valve (N.L.- Valve). Can anyone point me in the right direction to find these parts new or used? Failing that where could I buy a used unit? Thanks, James Wagnon