have a '78 F150 -351 with C-6. Standard 2bbl .
does anyone have the original Ford part # for the throttle solenoid so I can go to a parts place and get one . If you have this part and would like to get ride of it even better, my carb. is looking for a little helper lol . I have A/C and no solenoid to bump the rpms for A/C operation and I live in AZ.
thanks for any info. !!!

 

On these era engines, the solenoid is not meant to increase idle speed when the AC is on. If your RPMs are too low when the AC is on, check the idle speed, idle mixture, and timing. Idle mixture can be dialed in with a vacuum gauge.

Check out this thread for more information on the intended use of the solenoid:
https://www.ford-trucks.com/forums/1...ml#post9974068

Of course, that's not to say you couldn't wire it the way you're describing if you absolutely needed it that way.

 

did a tune up before along with timming gun, vacuum guage and rpm guage hooked up. Had it all dialed in then had A/C compressor replaced and was told that carb was missing the part to bump the rpms up when A/C was engaged. So went looking for the part that compensated for the extra drag of A/C

 

the carb has a anti-stall dashpot on the fire wall side of the carb . on the grill side it seems to be missing this solenoid that I guess would be elec. activated with the A/C .
If its not for this then I am at a loss as to what bumps the rpms up when you use A/C

 

My 74 has this solenoid and the only time power is applied to it is when the AC is turned on, the wiring to this solenoid is tied into the factory wiring harness from dealer and not the back yard mechanic.

 

Shown below is a 1976-78 wiring diagram. The diagram clearly shows that the idle stop solenoid (referred to as "throttle solenoid" in the diagram in the lower left-hand corner) is intended to be powered through a fuse from the same hot-in-RUN signal from the ignition switch that powers the "I" terminal of the regulator for an ALT light setup, and not from the heater controls. Therefore it's engaged any time the key is in RUN.

If your solenoid is powered otherwise, then it's part of some setup that I'm not aware of, and deviates from the diagram below. The diagram is what it is. If you think it's wrong, take it up with Haynes, or whoever it is that Autozone's website gets them from. I have never seen it wired otherwise during these model years; as such there was not a means to raise the idle only when the AC was engaged from what I've seen. My '79 F100, '73 Galaxie, and '77 LTD each have/had AC, as well as an idle stop solenoid, and in each case, the solenoid is powered from hot-in-RUN as the diagram suggests. And while the last two vehicles aren't trucks, many of the principles (and even wire colors in many cases) are the same among all three.

 

I have this same issue with my truck, and another user (can't remember his name) does too. Last year I just got to where when I came to a red light / stop sign I'd flick it to vent to disengage the compressor and put it back to A/C when I took off. Not very practical or correct but it worked. I'm going to replace my York compressor with a newer smaller compressor this year before it gets hot though, so hopefully I can't feel all that vibration or drag the big York causes.

I know none of that is any help! LOL

 

fmc 400
so what you are saying is the idle will be at 1000 or so when the engine is running since the solenoid will be active and setting the warm idle screw at about 650 or so doesnt matter because when the key is active the solenoid will push idle up past the warm setting so A/C is not a drag on engine?

 

rdweathers
would you be able to explain more as to the wiring diagram on your engine

 

However you hook it up, the solenoid is an obsolete part. The wire on mine was brittle and falling apart so I looked to replace it. No parts house has them anymore. You will have to search the internet high and low to find one. I saw a few on E-bay a few months back, but they were charging your first born. I ended up soldering a new wire to it.