pcolt94

I have had this random situation several years and finally got a handle on it. Problem was clutch would not engage. This would happen at random times on initial A/C startup but would stay working and cycling once I got it going. If I shut down the engine and did a restart, I could get it to work OK most of the time. Been riding around with a DVM in the car connected to various points trying to see what was happening and possible see a pattern. I tried to see what the cycling switch, programmer, PCM and compressor was doing at the time of the failure. Data was very slow to get .

I actually thought the PCM was not closing the A/C relay but ended up at the compressor clutch. It got voltage but would not pull in quickly enough. Basically it was lazy (from age) and wanted a specific voltage range. Because of its age, the clutch like to see 12.5 volts or more. It will close at 12 volts sometimes but never under 12 volts. I powered the clutch with an external power supply so I could see the range it worked in. Temperature is probably a factor as well.

So here's what was happening. If the voltage is applied thru the system and it does not energize the clutch, the high pressure switch does not see a change in pressure in a specified amount of time it sets code 67 (no MIL lamp). At that point the PCM will not give the command to the AC relay to close ever again no matter how many times you push the buttons on the controller. The code stays in the PCM but if you shut the engine down it resets and will then give the command to close the AC relay again.

The system looses about 1.5 to 2.0 volts thru the wiring in the harness. I checked the voltage drop across the fuse, AC relay and connector on compressor and it's small, .01 or .02. If the compressor was new it would not be a factor since it should snap close with only about 10 volts to it.

To add to the complexity of the problem, when first start of the day, the charging voltage is its highest since it has been sitting over night or longer so voltage is in the 14.8 or so. After running for a while charging voltage drops as battery is charged and drops to14.0 or so.

So with a charged battery and the voltage drop the clutch may not get enough voltage to energize it fast enough hence no pressure change, the code gets set and the AC will not come on till a restart and you get lucky. Worse at night obviously with the headlights on.

So now I know what I'm dealing with. Don’t have a true fix and not running out to replace compressor or clutch since it works most of the time. If I can't get more voltage to the compressor maybe I can get an better ground and gain a little on the other end.
We'll see how creative I can get.

antfarmer2

is your freon low? spit in the fill valve and look for bubbles. try jumping your pressure switch and see if it kicks on. look for loose or dirty connections.

93Rubie

If you seeing a 1.5-2.0 drop in voltage from the battery to the a/c clutch, right there is your problem. Find your drop and you found your problem. Test the wiring not just the components.

Also if the a/c clutch has a lot of wear air gap could be a factor I suppose.

pcolt94

There are no valve leaks and have no connector problems. I have tracked this problem for a long time now and know exactly what happening. I know the pressure switch is working right as I have monitored every point with a voltmeter and a Tech1. As I stated this is what's happening a took a while to understand and put the puzzle together.

But thanks for the input anyway.
On the other side of the coin, just recently my evaporator started leaking so in the process of collecting parts now and getting ready but no rush to do it. Have dye in the system and can see it coming out at top and bottom and valves look fine. If you missed it, there's a thread for it.

antfarmer2

great sounds like you found your leak.

ghlkal

Thanks for taking the time to outline this issue

I'm dealing with something similar and these intermittent issues take a while to diagnose.

pcolt94

This being my thread, and came across it again, I had a resolution recently to the problem. First let me say all the above information is correct. I did not have defective wiring, it just the design of the car.

I was reading some other threads and came upon some where people were able to remove the AC clutch with the compressor installed. It got me curious and decided to explore some options.

I measured the clutch gap and it looked OK but a bit big. So I removed the clutch hub but could not clear the pipes. It seems on my car the pipes have a slightly different bend and the hub would not clear. Working in a small space, and encountering some other problems I was able to work it out.

In the end I removed the 3 spacers and after measuring them re-installed 2 spacers. Assembled the hub and made a gap measurement. Still in spec but a bit tighter as what my goal was.

I tested it with a external power supply to see the improvement. It worked great. It now locks up at 10 volts with ease so the voltage the car provides is no problem now. When I press the AC button, the clutch snaps right in with no hesitation as before.

So in the end, Ruby 93 was right on target as I circled back to his comment years later.

My recent thread on the current repair.
https://www.corvetteforum.com/forums...le-on-car.html