Could some one tell me why my rpm drops down to 500rpm when I turn on my ac. If it matters it is an LT1. When off it idles at 1000- 900rpm. I know it should only drop about 100rpm. How do I fix it?
Thank's Rob
Thank's Rob
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Re: C3 (72) AC
1000 -> 500 RPM is QUITE a drop! In my experience, a real McCoy Corvette A/C compressor in good repair should only load the engine about 175 RPM...
Now, the core A6 used in that period for Corvette was different than the equivalent passenger car A6. The Corvette A6 had an internal displacement of 10.8 cu-in while the lion's share of the rest of the Chevy line-up used an A6 with larger 12.6 cu-in displacement. My hunch is that would add more drag when the compressor engages...
The major non-AC Delco sources who rebuild compressors (Four Seasons, NAPA, Etc.) don't really distinguish between Corvette and pass car. Check their catalogs and you'll find they use the same proprietary PN for both applications. This suggests you might have a larger displacement passenger car compressor on your car, if the original failed and was replaced with a rebuilt aftermarket A6...
What to do? There's not much you can do. The design of the emissions control system did NOT use intelligence to fire the carb's idle solenoid & bump engine RPM based on compressor ON/OFF! They anticipated the native drag of the compressor would be within a tolerable window and the car wouldn't stall under worst case conditions (foot on brake, engine at idle) with the proper tune up and correct factory/stock parts.... -
Re: C3 (72) AC
Have you checked other components, for example is the vacuum advance pull-in too high relative to the spec, causing the engine to lose timing when the load is applied by the compressor?Bill Clupper #618Comment
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Re: C3 (72) AC
Jack & Bill,
Thank you. To my beleaf the compresser is still te origanal to then car.
At one point some one put in brackerless ingnition. I am going to put it back the way it came. I will check the timeing tomorrow. When I got the car back in March it did not do that. It started Just before the front bearing went on the compresser.
RobComment
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Re: C3 (72) AC
Jack
What do you mean when you said "is the vacum advance pull-in too high".
RobComment
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Re: C3 (72) AC
I didn't say that...it's Bill Clupper you're responding to...
Let me guess, Clup might have been asking if the vac advance on your distributor was the correct, factory original, 1973437 component designed for low RPM stability with the '71 CEC and '72 TCS emission system that 'switched' vacuum to the distributor based up what gear the transmission was in.... These had a pretty 'flat' low RPM response range designed to be tolerant of going quickly to 0-degree advance under curb idle operation.
You'd see the last three digits of the PN (437) embossed on the vac advance's mounting arm along with the advance mech's max advance profile (015 or 15-degrees) embossed next to it by looking from the top of the distributor down (with cap removed) and behind the vac advance can. Later era Delco generic service replacements will be embossed 'B22' on the arm in lieu of the two number sequence emboss described.
I'd further venture to say Clup was suggesting the loading of the A6 compressor might be enough to FINALY collapse the vac advance on a 'clone' can vs. a real McCoy factory production original vac advance can thus exaggerating the idle RPM differential you see with and without A/C active.
But, Clup is the best source to answer your question as it was he who posted the input/question & not me...Comment
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Re: C3 (72) AC
Bill,
In my last respons, could you elaberate.
Thank you RobComment
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Re: C3 (72) AC
Thank you Jack,Next time I will try not to get the names mixed up.
Thank you again for the imput.
RobComment
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