NJRob

Ok, I am going to try and explain this the best I can. I have a 77 olds 350 in my 71 vista cruiser. I found that there is an ac solenoid on the drivers side of the quadrant 4bbl carb. Can anyone tell me how it works and if I need it to control the ac in my car? Also the compressor says R12 refrigerant. How can I tell if the compressor is from the 77 engine or the 71 engine.

joe_padavano

The solenoid is simply an idle "kicker" that slightly increases the throttle opening at idle when the A/C compressor is on. It is not required for the A/C to function. It's typically wired in parallel with the A/C compressor clutch so that the solenoid is energized any time the clutch is engaged. The extra drag of the A/C compressor can lower idle speed and sometimes cause stalling. Note that use of the solenoid was usually a bandaid measure for mid-70s engines with early smog equipment. If your car runs fine without the idle kicker, don't worry about it. If the A/C causes the idle to get too low, connect it.

Note that there were two different uses of the solenoid, one to increase idle speed when the A/C was engaged, as I noted above, and the other as an anti-diesel feature. The lean mixtures and haphazard smog equipment used on the 1970s motors often led to dieseling at shutdown. In that case, the solenoid was energized any time the ignition was in the RUN position and the solenoid adjusting screw was used to set the normal idle speed. When the key was turned off, the solenoid would de-energize, allowing the throttle blades to completely close and prevent dieseling. Again, if your car is running fine without it, don't worry about it.

I suspect that the A/C compressor you have is the one that came with your car, though frankly it doesn't matter. Both years should have used the large A6 compressor, which is designed for R12 but will work with R134.

NJRob

Awesome, thanks for the info.