A/C Retrofitted,... Now My Idle is too high...

[The Machinist]

I had my A/C retrofitted to run R134a today, and when I got home from work and went out to check it out, I noticed that the idle speed was waaaaay too high. It was idling at about 1,000-1,100 with the A/C off, and with it on at about 800-900. Before I took it to the shop it idled at 800-900, which I knew was a little high.

I just had a conversation with Klinetime574 on facebook about this problem, and he told me that there is something on the carb that kicks up the idle speed when the A/C compressor switches on, but I cant seem to find anything in my service manuals. I have been reading up on idle speed adjustment though. Any tips for doing this?

It says to "break" the idle limiter cap... breaking things never seems like a good idea when I don't have a replacement, could someone elaborate on this?

Thanks for the help!

 

[2mbb]

The AC idle up circuit is not well documented in the FSM. There is some component troubleshooting in the AC section of the body and chassis manual.

The attached PDF shows the vacuum routing for that parts the increase the idle speed when the AC compressor turns on. The vacuum source is at the rear of the intake manifold where the brake booster also gets it's vacuum. The VSV is located on the drivers side fender well and the vacuum diaphragm is located on the front of the carburetor. If the vacuum hoses are connected wrong on the VSV (if the hoses are switched), then you might get the condition you describe. When properly connected, the VSV port that is connected to the diaphragm is either vented to atmosphere (AC off) or connected to intake manifold vacuum (AC on). If the vacuum hoses are reversed, then when the AC is off, the line to the intake manifold will be connected to the atmosphere, leaning out the A/F mixture causing the idle speed to increase.

I think the procedure you were reading that refers to the idle limiter cap is for setting the idle mixture and speed. On documented procedure I use is called the Lean Drop method (described in the 2F engine and 2F emissions manuals). This procedure is not really going to help your condition because there are separate components that increase the idle speed when the AC compressor turns on. However, the idle limiter cap was installed at the factory to prevent major adjustment of the idle mixture speed (probably another emissions control feature). On a car this age, these caps are usually long gone and are not required to be replaced (at least no smog inspector has ever challenged me because I don't have one). Another method that was employed was to cover the hole where the idle mixture screw sits with a lead plug, requiring that the plug be drilled out to change the idle mixture.

 

[TallCanDan]

The AC idle up circuit is not well documented in the FSM. There is some component troubleshooting in the AC section of the body and chassis manual.

The attached PDF shows the vacuum routing for that parts the increase the idle speed when the AC compressor turns on. The vacuum source is at the rear of the intake manifold where the brake booster also gets it's vacuum. The VSV is located on the drivers side fender well and the vacuum diaphragm is located on the front of the carburetor. If the vacuum hoses are connected wrong on the VSV (if the hoses are switched), then you might get the condition you describe. When properly connected, the VSV port that is connected to the diaphragm is either vented to atmosphere (AC off) or connected to intake manifold vacuum (AC on). If the vacuum hoses are reversed, then when the AC is off, the line to the intake manifold will be connected to the atmosphere, leaning out the A/F mixture causing the idle speed to increase.

2mbb- I don't see anything attached... Very informative none the less.


Danny

 

[2mbb]

2mbb- I don't see anything attached... Very informative none the less.


Danny

hmm. There is an attached file--not a picture, but a PDF file. It has an Adobe icon with a file name "AC Vacuum Piping.pdf" inside a box that says "attached images". You would click on the file name to download the PDF. At least that's what I see when I view the thread.

 

[The Machinist]

Thats the ticket! Turns out my vacuum lines were backwards, now it idles where it should, and when the compressor kicks in, it stays about the same.

I think this was causing my high idle before I got the A/C fixed, because before it would idle around 850-900, and now its 650-750.

Thanks 2mbb!