My 72 vette has a crate 350 engine with all new A/C components. The previous owner put all the hardware in it and told me when I bought it that the a/c worked but seemed to have a leak and needed to be looked-over.

So I had it serviced this week, which included vaccuum, r134 fill-up, and a new belt had to be put on since there was no belt on it before.

The first drive out I noticed while idling at a stop sign with the a/c on (tried "Max" and "Norm" settings) that the battery gauge was going nuts (needle was jumping around over and under 0).

I had to hold a bit of pressure on the gas pedal to keep the engine running - it seemed likely to quit on me while idling, even after being warmed up.

When actually out on the road, if I was just cruising the battery meter was stable, but I noticed a regular hesitation in the car, which, if I didn't know any better, I'd say felt like minor engine braking at regular intervals. If I switched off the a/c, the car ran smooth -

So -- I know running your a/c will put constraints on the engine but should it be doing all this?

My thoughts are maybe the belt the tech put on isn't right somehow, or maybe I have a problem with my electrical system...?

Any ideas on where to start troubleshooting this would be appreciated!

 

They may have placed too much refrigerant in the system. A characteristic of the compressor switching on and off pulling the engine down...

 

I would believe this part is normal though I do not have A/C. The reason I feel this is normal is that the alternator does not put out much at idle. The exact same thing happens to me at a stop sign with my turn signal on. I would think your compressor is cycling and everytime it energizes the clutch you see the jump on the gauge. I may be wrong since my car never had A/C, I wish it did.

 

Generally cars need something to kick up the idle when AC comes on. Do you have anything to kick up the idle when AC is on?

 

If you have the original A6 compressor, then I think it's absolutely normal to put a ton of load on the engine (I heard that it would take up to 30 HP!!). Did you flush clean all the A/C components and put a fresh R134a compatible refrigerant oil in there? .. if you put a R134a and mixed it with a non R134a compatible oil then chances are getting everything siezed up after a while (tell me how I know!).

 

up your idle a tad, a proper solenoid would be better since it only raises the idle when the a/c is on. Its should cycle off and on but not quickly

 

Sounds like you need an idle compensating solenoid. If you have the original carb it should be built into the carb. If not you can buy on from one of the vendors but they are expensive. It kicks up the idle when the A/C is on due to the extra load.

Make sure your car is tuned correctly and you have no vacuum leaks when in A/C mode. If the idle is seriously low your alternator can't put out enough and that's why the gauge is all fluctuating all over the place.

http://www.parts123.com/parts123/yb.dll?parta~partsort

 

I just finished rebuilding the a/c system recently in my '72 using all new parts. (sanden rear exit compressor,evaporator,drier,expansion valve,POA valve,parallel flow condenser, hoses, fittings and a new a/c wiring harness.) If you're using a stock POA valve the compressor should not be cycling on and off. I also found a idle solenoid at auto zone(part#E403) for $26.99. I still had the old bracket laying around so I wired the solenoid to come on whenever the a/c is turned on. In my case I don't think I really needed the solenoid because using the sanden compressor the idle only drops 100 rpms when I switch on the a/c. The first place to start would be to see which kind of POA valve the previous owner installed. Is it the stock one or one of the updated cycling POA valves? As I understand it, the A6 compressor does not take well to being cycled on and off. When I turn on my a/c, the compressor runs until I turn the a/c off. I don't know if this answered any of your questions but hope it helps.