AC idle bump not working

[1986bronobbt]

I have a 1986 bronco with the 351w high output.  It has a Holley carb that was just rebuilt. I know in the past it used to increase the idle for ac and now it doesn’t.  It will keep running but the rpms drop to around 500.  I was wondering how the ac idle bump works on these and where to look to troubleshoot this?

[Gary Lewis]

Welcome to the forum.  I was hoping you would do the introduction, as requested in the email.  But perhaps you will get to that as well as the requested signature in a bit?

The throttle-kicker circuitry is shown here: http://www.garysgaragemahal.com/carburetor-circuits1.html.  I'd start with checking to see if you are getting power to it when the A/C is on.

[Gary Lewis]

Actually, it isn't the "throttle kicker" but the "throttle position solenoid".  You can see it in the schematic below on the left in the middle.  Check that you have power on the light green/pink wire when the compressor is running.

[LARIAT 85]

Your truck should be able to idle at 500 RPM without any problems.  Do you have a wild aftermarket camshaft or something?

The A/C throttle kicker is designed to physically chock the throttle lever up a little to compensate for the extra load on the engine the A/C compressor imposes.  This way, you can set the curb idle as low as possible for normal conditions.  When the A/C compressor turns on, you can adjust the throttle kicker to push up on the throttle lever to achieve the same idle RPM as normal curb idle.

If your truck is at idle and you switch the A/C on, the throttle kicker will *not* push the throttle up by itself.  It works kind of like the choke cam in that the throttle kicker will hold the new throttle lever position only after you depress the throttle.

If you don't have the A/C throttle kicker, you will have to set the normal curb idle speed higher than necessary in order to compensate for the reduced RPM that occurs from the extra load of the A/C compressor.