80 gets the shivers when a/c kicks on, why?

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I am on my 4th 80 and I have to say this one has the coldest a/c. It’s a 94 if that matters, but when the a/c compressor kicks on it makes the whole rig shake. This is more pronounced when it’s in drive at idle compared to on park. When rolling of course cant feel it. Anyone encountered this? I thought maybe the engine mounts. Any ideas?

Tried doing a search but no results using several key words.

Thanks
 
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Because it's cold natured? brrr ;)

Sorry, bad joke but I'm prepping to replace most of the AC system in my 80 so wanted to join in to follow along and learn something.

I can add that I've overcharged mine to the point of it shutting down due to high pressure and it never shuddered noticeably so I would expect overcharging to be a secondary factor at most.

Also, I'm sure you are familiar with how the idle will kick up when the ac engages on an 80. Perhaps the shudder is related to that process and not to the AC system itself. Have you tried to manually increase the idle speed with just the gas pedal a comparable amount to what the ecu does when the AC engages? If you end up being able to do that and replicate the shuddering while the AC is not engaged you may be able to rule out some possibilities at least.

Good luck and once you get it sorted share more on your thoughts after owning 4 80s. Any cool drivetrain variants or comparison points etc. in your experience?
 
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Idling in Neutral
Photo 1. With a/c compressor off. 600ish
Photo 2. As it kick on it drops about below 600 RPM…. this is when it shakes
Photo 3. Once compressor is on it is over 800 RPM

Idling in Drive it is the same except that once compressor is on it goes back to about 600ish RPM. But again when it kicks on it drops RPM and I feel the shudder.
 
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Should be 650 +/- 50 with the compressor off, 900 with it on, in neutral. It should definitely never drop below 600 in neutral.

Remove your intake manifold and throttle body, clean them, and replace all your vacuum lines.

You can fiddle around with just the Idle Air Controller, but chances are the whole intake is blocked up with carbon, if the IAC is affected.
 
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So I replaced the throttle cable that was tired and stretched after 165k miles (pic below). Replacing it now keeps the RPMs within spec. When the a/c kicks on it drops for less than a second and revs up to spec. Given that it doesn’t fall below 600 rpm any time this eliminated the shudder I was feeling when the compressor kicks on idle in drive. Overall pretty easy fix with the write-up from NSGB Copied below.

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Thanks for all the input!
 
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I had exactly the same issue. Replaced my throttle cable this morning. The problem is gone and throttle response is much snappier. So happy you posted this thread.

I had purchased a throttle cable a while back because mine was crispy like yours, but never connected my AC idle issue to the cable. Super easy job to replace it.
 

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