EmTee Posted September 22, 2017 Share Posted September 22, 2017 When I attempted to turn on the A/C last Sunday on the way home from Lake George there was a horrible screeching sound. When I got home and raised the hood I could see that when the A/C was turned on the compressor clutch was slipping. Later I determined that the compressor was not locked-up, as I could turn the shaft using a wrench. Today I checked the voltage to the A/C clutch and measured only 10.2 Volts. I verified a good ground connection (same reading at the negative battery post). So, I suspect a bad clutch relay, but following the wiring back doesn't lead me to a relay before the wires head into the cabin. There are two relays on the firewall, however, neither of them have the green clutch wire on them. Can someone tell me where the A/C clutch relay is located? Thanks in advance for any assistance! -Tim Link to comment Share on other sites More sharing options...
Seafoam65 Posted September 22, 2017 Share Posted September 22, 2017 60's GM cars do not utilize a clutch relay.......the power comes directly from the switches in the dash. You probably have a voltage drop at the switches or their connectors. That being said, usually the clutches slip on A6 compressors because the head pressure is going too high due to restricted refrigerant flow. If the clutch is actually kicking in, it shouldn't be slipping because of voltage being a volt low. You need to put guages on the system and check the pressures. Link to comment Share on other sites More sharing options...
PWB Posted September 22, 2017 Share Posted September 22, 2017 (edited) I'd say 10.2 volts be sufficient Tim. In addendum to Seafoam's comments - hows the belt? I switched to new "nibbed" belts, re-tension and it made a difference. Eliminated the screech. Edited September 22, 2017 by PWB (see edit history) Link to comment Share on other sites More sharing options...
JZRIV Posted September 22, 2017 Share Posted September 22, 2017 Tim, Run a jumper from battery to clutch and see if anything changes. The belt is also another possibility as Paul mentioned. Some later model belts just don't seem to grip as good when running these power hog compressors. Link to comment Share on other sites More sharing options...
EmTee Posted September 23, 2017 Author Share Posted September 23, 2017 OK, I'll check the belt and then try jumping 12 Volts to the clutch to see whether it makes a difference. It doesn't seem like a head pressure issue to me because it happens immediately when I engage the A/C; it's not like the compressor spins for a minute and then starts squealing... Link to comment Share on other sites More sharing options...
Seafoam65 Posted September 23, 2017 Share Posted September 23, 2017 If the system is totally plugged up where freon can't circulate, the high side can hit 450 psi in just 5 seconds. Link to comment Share on other sites More sharing options...
EmTee Posted September 24, 2017 Author Share Posted September 24, 2017 UPDATE: First, I checked the A/C belt tension and it was loose, so I tightened it until I had approximately 1/2" deflection when I pressed the belt midway between the A/C and crankshaft pulleys. After I did that I noticed that the washer on the forward compressor tension lock bolt was now essentially aligned with witness marks in the adjuster bracket that runs from the top of the compressor to the intake manifold (a good sign). Next, I fired up the engine and tried engaging the A/C. At this point the compressor was turning and cold air began blowing out of the dashboard vents -- all is well! With the A/C running I re-checked the voltage at the compressor clutch and measured 13 Volts (voltage at the battery terminals was 14.7). The previous voltage measurements were taken with the engine off (battery voltage was 12.5). So, it turns out that the entire issue was a loose A/C belt. I was surprised because even the 'loose' belt seemed as though it wasn't really that loose... I had recently removed the upper compressor bracket so that I could paint the engine, When I re-installed the bracket I tightened the belt an amount I thought would be sufficient without placing excessive strain on the water pump bearing. I never turned-on the A/C until last Sunday. Anyway, the long story short is I created the issue by having insufficient tension on the belt. That said, although the A/C is now working as before, I did notice a steady stream of bubbles in the sight glass. I did not run the A/C more than 3 or 4 minutes, but I think I need to find someone who can put gauges on the system and check the refrigerant fill level. The system is still running with R-12. I should probably try to snag a couple of cans of R-12 on E-bay. Thanks to Winston, PWB and Jason for your input. I'm glad that for once the issue turned-out to be something simple! 1 Link to comment Share on other sites More sharing options...
telriv Posted September 24, 2017 Share Posted September 24, 2017 One thing no body ever does is ADD OIL to the system. This is one of the things that causes compressor failures. When Freon leaks out so does the oil. Add at least two (2) ounces. 2 Link to comment Share on other sites More sharing options...
60FlatTop Posted September 24, 2017 Share Posted September 24, 2017 Jeez, that reminds me, I have new belts for my '60 hanging in the garage, just steering and alternator, but I keep forgetting to swap out in 15 year old ones. Good job before lunch. Bernie Link to comment Share on other sites More sharing options...
rocky5517 Posted September 24, 2017 Share Posted September 24, 2017 When I bought my (67) car it still had R-12 . A mechanic switched to R-34 but I know he didn't flush the system properly.. He added PAG oil. Then we saw the muffler was bad, so I had a welder just chop off the bottom and re-weld it back together,. No problem. Installed an upgrade from Vintage Air, and re-installed R-12. Once in a while a would hear a squeal if I engaged it at high speed but haven't heard it lately. It may have had too much R-12. But I have two kinds of oil in the system- the original mineral oil, and the PAG oil. I go to a lot of cruise nites, show etc, and I ask good mechanics ( or at least I think they're good) should I flush the system and put in mineral oil. Everyone asks me - " how is it working?" I say, "Fine". On a real hot and humid day I notice it loses a little punch after an hour or so, but it doesn't bother me. It seems exactly HALF of the guys say to flush it, and the other half say leave well enough alone. I have sided with the latter group, because, well, that's what I was hoping to hear. Link to comment Share on other sites More sharing options...
60FlatTop Posted September 24, 2017 Share Posted September 24, 2017 Don Rumsfeild's recent book just hit our bathroom shelf. Don says if everyone agrees it's wrong. You're good. Bernie 1 Link to comment Share on other sites More sharing options...
PWB Posted September 24, 2017 Share Posted September 24, 2017 Quite amazing system from '67. I still have R-12. I won't change a thing in my arctic blaster. Link to comment Share on other sites More sharing options...
EmTee Posted September 25, 2017 Author Share Posted September 25, 2017 Agree with Paul -- I want to stick with R-12 as long as I can. I also agree that adding a couple of ounces of oil when I finally do get it topped-off is a good idea. There is evidence of some oil film at the front of the compressor, so I'm sure some oil had escaped over the last 50 years... Link to comment Share on other sites More sharing options...
telriv Posted September 25, 2017 Share Posted September 25, 2017 Of course there's no way to know how much oil has been lost through the front seal so I think in that case you should add 4ozs. just my thoughts. 1 Link to comment Share on other sites More sharing options...
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