We have a 1968 Corvette with astro-ventilation system in it, last summer after having a cart Engine. installed my wife wanted the air-conditioning fixed also! The mechanic told me which parts to order which I did, a new compressor exactly like the one that was in the car when we bought it, dryer, and a POA low pressure valve, he also replaced one hose from the condenser to the compressor and flushed out the entire system and all of the other hoses and other parts. The system works OK as long as you don't drive the car over 3300 RPM. At this speed it misses, backfires, and sounds like it is going to jump off the road. So far I have replaced the distributor cap,  rotor button, condenser, coil, wire from the starter to the coil, and last but not least a new battery, I also had the alternator checked it is putting out 14.8 volts. it still does the same thing at 3300 RPM. My wife will ride in the car during the winter as long as there is heat, so I unplugged the compressor, we have heat but know astro-ventilation system. Which of course means that I have about 4 mouths to figure out why the system is not working the way it is suppose to.

Does it run OK with the comperssor unplugged?

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Hi; It runs OK with the air-condition unplugged. The air-conditioning system didn't work on the car before we had it repaired, it was all there but the compressor made a lot of noise when we charged it up. It still misses when the compressor is plugged in if the car is parked and run over 3000 RPM.

This is a continuation of another thread...
Did you do the last thing that Ken suggested, which was removing the A/C belt, plugging the compressor back in, and trying it like that?

If the engine is only missing with the compressor plugged in, with the A/C off, there has to be an issue with how the compressor is wired. My wiring diagram does not show the A/C system, so I may have to look a little deeper to find one that does.

If I understand, the car runs fine with the compressor unplugged, but the blower blowing, correct? In other words, as long as the compressor is unplugged, there is no problem? Doesn't matter what position the heat-A/C switch is in, or the blower?
OR..is it only with the A/C on?

Keep in mind, the compressor will also engage with the defroster on.
Does the compressor shut off when you turn the switch to "Vent" or "Heat", or does it run all the time?

So many questions...

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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Hi Joel;

Hi Joel;

Where did you add the other "ground" wire? And, more importantly, why?

The compressor should only have two wires, the green and black, as you stated it had. The green wire is power from the A/C switch, and the black wire is grounded to the compressor bracket. The early cars, like yours, should also have a thermal limit device in-line on the ground side. It doesn't have to have it, but it saved the compressor in case of an overheat condition. What it would do is act as a fuse. If the wire for the compressor got too hot, the limit would open, and kill power to the compressor. Too much heat could be from a short in the elector-magnet that engages the compressor clutch, or even from the compressor not cycling on/off as it should.

You may well have a compressor clutch that is malfunctioning/drawing too many amps, causing the problem.

What Ken suggested, as far as removing the belt, was to see if the compressor was causing fluctuations in the crankshaft rotation, which could cause the timing to jump around, if the timing chain/gears had some wear/slack. The same could be said if the bearing for the compressor pulley was too tight, or failing, but they normally make a noticeable noise when that happens.
Also, with the belt off, and the compressor plugged in, it would tell if there was an electrical issue with the compressor, or a mechanical one. With the belt off, and the A/C on, if there is no engine miss, then problem would be compressor related. If the miss still exists with the belt off, it is an electrical issue.

I hope some of this helps!

btw...the compressor should not run in any position except "A/C, or "Defrost". If is does, then that is another electrical problem we'll have to figure out.Adams' Apple2007-12-01 09:00:52

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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Hi Joel;

I'm not sure if this is the case but some systems have a circuit that shuts of the a/c at a determined rpm to help with power. Not an a/c spcialist but passing on what little I know. shelly 81

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