Hi Everyone, have been reading the postings for over a year now, and recently decided to register. I must say you all are certainly a knowledgeable group of Corvette junkies!!
Hope you can help me out. I have a '68 coupe, rebuilt numbers match 427/400 4spd. tri-power w/ A/C, 87K miles. I live in Houston. Had the car out last Fri nite. About 20 minutes into the drive, w/ A/C cranked, engine started to sputter (low idle) when at a stop. Lights were on. Had to hit gas to keep it running. I'm used to some amp draw under these conditions, but idle RPM went under 5 (normally around 8-9). On way home under same conditions, car stalled and could not get it started (had to get it jumped). It runs fine w/ A/C off, but w/ it on (incl. lights and radio), was running -10 on ammeter at idle and just around zero at acceleration. Is this normal, or is it the start of a diminishing alternator? Have not had the problem under similar conditions until last Fri nite.
Also, why is it so hard to start when warm?. It'll crank for a second, go dead for a second, then reluctantly cranks until it turns over. First time have had to jump it the other nite when trying to start it warm. After this incident, it started fine the next day.
Appreciate your thoughts!

Pete

 

Nice 'Vette!....The a/c doesn't draw too much, but the blower motor does. The a/c does load the engine, though. You should have an idle solenoid on the carburetor which raises the idle when the a/c is on. This will cure the low idle speed problem as well as help keep the battery charged. You may need to also have the battery/charging system checked. The starter may also be experiencing "heat-soak". Have it checked also. Always try to keep the ammeter on the positive side, even if that means turning the a/c off. (I know...I used to live in Houston)....
Hmmm....Not sure if the 3X2 units used an idle solenoid....

 

Sounds like the compressor locked.

 

Thanks big_G, not sure on idle solenoid on Holley, will check into that. I did though increase the idle manually last nite and tested under similar conditions and had better results. Just not sure why it started now and not before when I loaded w/ a/c, lights, etc. and did not have to adjust the idle.
Tell me more about "heat-soak"? Would that require the purchase of a new starter, maybe heavy duty variety (if there is such a thing)?

 

I just installed an idle solenoid on my vette as I was having the same problem,It does help.

 

The warm start problem could either be the classic GM starter heat soak problem or a bad connection. First clean your power connections - frame grounds, battery terminals, starter terminals, etc. If that doesn't fix it, time for a new or rebuilt starter.

The A/C on problem still sounds like a locked-up compressor to me. I had that happen to me twice on my old Talon - the compressor would lock up, it would drag hard on the engine, then the belt would shred into nothingness while I was trying to figure out what the heck was going wrong.

 

Check your charging system first before the a/c.
Using the a/c draws a lot more current and along with other elec demands can slowly drain the battery. Also the a/c use will create more heat under the hood.

As mentioned previously, clean all your big terminals and check the output of the alternator both at high idle and cruise speed. Also do a load test on your battery. Free tests at some parts stores. You may have to go to a bigger alternator if yours is too small.

 

Just checked the A.I.M......L-68's with A/C have an idle solenoid for the center carburetor. With the engine and a/c on, adjust the bolt on the solenoid to achieve 1,000 rpm. You may have to blip the throttle to let the solenoid plunger extend.

 

With Noonie. Sounds like more than one problem. The Amp draw -10 on the gauge means the alternator is not keeping up with everything at idle, not real uncommon and your correct it might be an indication of a dieing charging system. I think that alternator is internally regulated, there are 3 pairs of diodes in there that give up eventually, loss of any of them means lower charge capacity. You can pull the alt and get it checked.
Batman is correct about the connections, you need to go thru them all to make sure your ok, battery connections, frame grounds, starter connections, and the big wire on the back of the alternator.
If the AC is working, the compressor is not locked, but could be dragging the engine down at idle more than it used to because of a tuning issue (plugs, cap, rotor, etc..) might not be bad enough to miss normally but at idle with the ac on just a small reduction in HP.
The starter might be the culprit in the hard start issue (along with a mostly discharged battery from other problems) Go thru all the other stuff and eliminate them first, then deal with the starter heat soak issue.

 

You may not have a current draw issue but an issue the compressor just plain bogging the engine. I believe there is some kind of vacuum module that ticks up the fuel flow to the carburator a bit to compensate when turning on the air. I would check my GM manual, but I am at work and have no access to it. I would think if you had a current overdraw you would blow the fuse. If the compressor clutch is binding, logic would say that the current to drive the motor should rise considerably and pop the fuse. I suspect more the subsystem that helps adjust the RPM when the compressor turns on.

 

Thanks all for the suggestions. Will check/clean all elec. system connections and get the battery and alt. tested this weekend. A/C continues to blow cold thru all of this, so I think the compressor is okay. The idle solenoid concept makes sense as when I increased the base idle speed and did the a/c, lights, etc. thing, all seemed well (at least there was not sudden dip in rpm). I check Paragon but did not see a part listed as an idle solenoid (looking for picture so I know what I'm adjusting), nor does it mention or show it in my service manual. As for warm start issue, I'll hope that clean connections and/or new alt./battery help this issue (will clean connection on starter also). If not, guess I'll try a new/rebuilt starter.
Thanks again for the assistance!!

 

Here is a post by BarryK that links to his solenoid pics.

http://forums.corvetteforum.com/show...8&postcount=45

You can get the solenoid at any parts store, most Gm cars from the late sixties until modern fuel injection used them. Check any old car junk yards, you will need the mount plate too.