Noise after AC service

[freakyhead94]

I attached a picture of a kind of similar low side gauge that was on my MGS. I unfortunately did not make a photo of it. I already returned it because I could not calibrate it. But there you see that the positive pressure range is measured in psi or bar, and the green vacuum section in inhg or bar. Mine looked the same and did not go lower than 27inhg.

[tbirdtbird]

Ok, now I get it.
Unfortunately the green vacuum part of the gauge is an unreliable estimate of vacuum. That vacuum reading is a throwback to the days of old with R12 where you could never go wrong no matter how bad a technician you were.
Please ignore it.
Lacking a vacuum gauge, if you are going to pull a vacuum, then vac for at least an hour.

Heck, in the old days, technicians just hooked up the R12 canister and blew it through the entire system never even bothering with pulling a vac.
Lots of R12 blown into the environment. Heck they even used R12 canisters to blow off condensers (instead of compressed air they had to tote up onto the roof.)
I know of several technicians who retired when all the new environmental regs came down because their job just became way more complicated.

The most important thing you can do with a gauge is to zero it out to zero pressure with the little adjustment screw so that your psi or Barr is correct. Forget the green zone

[JohnHere]

One point of clarification on the pictured gauge is that BAR refers only to the black-on-white outermost ring of calibrations on the gauge face, not to the white-on-green vacuum scale, which reads only in inches of mercury, or inHg.

[tbirdtbird]

True and interesting to note that minus 1 BAR on the dial equates to 30 in Hg on the psi scale

[freakyhead94]

I will do a third try with the vacuum. Tomorrow i will fly to Greece for vacation on a sailing boat with a group of friends. After that, I'll order another proper vacuum pump, gauge set and an additional calibrated vacuum gauge. I think I found good parts at an AC shop. The internet is full of crap.

Double the price of what I had before, but if it works, who cares...

I will report the results.

[JohnHere]

True and interesting to note that minus 1 BAR on the dial equates to 30 in Hg on the psi scale

I noticed that as well, although (and I could be off base here) I don't think the BAR scale is specifically intended for measuring vacuum from 0 BAR to –1 BAR. I believe only the small white-on-green (inHg) scale is. The white-on-blue scale gives PSI readings, which we're much more familiar with here in the USA. That gauge needs zeroing, though.

[tbirdtbird]

Agree. The -1BAR and 30In HG scale are no substitute for a proper vac gauge, as you know. The fact that those scales are on the gauge gives the owner a false sense of accuracy

[freakyhead94]

Quick follow up:

I changed the compressor, along with flushing the system, new accumulator, new orifice, new serpentine belt, o-rings and valve cores.

After removing the compressor, i tried draining oil from it and not a single drop of oil came out. Looking into the suction port, the inside also looked pretty dry. The compressor was oily on the outside, propably lost all it's oil. There was even oil on the belt tensioner and coolant overflow tank.
I also discovered that the previous shop installed the orifice tube the wrong way. I could barely get it out with some long pliers while heating up the pipe, because the tube was shoved into the 90° bend in the pipe.

I flushed the system with about a gallon of AC flush solvent and noticed black oil and metal scrapings coming out, also in the filter of the orifice. So the compressor was definitely on its way out, propably short before locking up. I wonder how the system even cooled that good at the end.

For anybody interested: I used one of those new style R4 scroll compressors. I list the part numbers at the end, because the manufacturer actually says that for a 1989 Caprice, there is no scroll version available, only the piston version. But I compared both compressors and the only difference is the pulley diameter. The scroll version I used is officially for a 1989 C1500 with a 4.33inch pulley like the original.
On my 89 Caprice, the clutch diameter is 5", which results in a 15% higher compressor rpm and the need of a 0.5 to 1" shorter belt. Fits perfect.

Drained the oil from the new compressor and added fresh 6oz of PAG46 as required, 3oz in compressor, 3oz in accumulator. (PAG46 for compressor manufacturer, 6oz GM service manual/underhood sticker). I also installed a high pressure cutout switch in the port on the compressor. It is not wired yet, ran out of time that day, but I will do that the next days.

Given that I read many times about a lower output of the scroll version, the higher rpm should come in handy. Since that 305 almost always runs a bit above idle while cruising, there shouldn't be a problem.

So far I really like the compressor. It is absolutely silent, even standing directly in front of the open hood with it running, it makes almost no noise. Only the click of the clutch is audible, nothing compared to the piston R4.

The noise in my original post is completely gone. The AC works silent as can be inside the cab. Maybe because the orifice tube was installed wrong?

System cools very good, I will test it again this weekend, forecast says 88°F.

Part numbers:
Compressor: UAC CO11169MC-KTAC (I received a CO11169-MAC, which seems to be the same, just another part number. Spoke to the company)
Orifice: AC Delco 15-5754
HPCO switch: Four Seasons 35961
Accumulator: AC Delco 15-1647
Belt: Optibelt 6PK2373 (available in Germany, maybe needs research for US)
Valves: Four Seasons 26777
Gasket Set: Four Seasons 26734 (make sure special compressor-to-hoseblock gaskets are included with the compressor)

[JohnHere]

After removing the compressor, i tried draining oil from it and not a single drop of oil came out. Looking into the suction port, the inside also looked pretty dry. The compressor was oily on the outside, propably lost all it's oil. There was even oil on the belt tensioner and coolant overflow tank.

Not surprised about the oil staining on the outside. R4 compressors do have a tendency to leak around the large o-ring sealing the outer shell to the inner compressor case.

I also discovered that the previous shop installed the orifice tube the wrong way. I could barely get it out with some long pliers while heating up the pipe, because the tube was shoved into the 90° bend in the pipe.

It's not the first time I've seen or heard of the OT being installed incorrectly. Surprised that a shop did it, though.

For anybody interested: I used one of those new style R4 scroll compressors. I list the part numbers at the end, because the manufacturer actually says that for a 1989 Caprice, there is no scroll version available, only the piston version. But I compared both compressors and the only difference is the pulley diameter. The scroll version I used is officially for a 1989 C1500 with a 4.33inch pulley like the original.
On my 89 Caprice, the clutch diameter is 5", which results in a 15% higher compressor rpm and the need of a 0.5 to 1" shorter belt. Fits perfect.

I've heard about the existence of both R4 piston compressors and the R4 scroll variant, but I've never replaced a piston version with a scroll version. Please let us know how it works out.

Given that I read many times about a lower output of the scroll version, the higher rpm should come in handy. Since that 305 almost always runs a bit above idle while cruising, there shouldn't be a problem.

A little extra RPM will probably help cooling, especially while standing still at idle.

So far I really like the compressor. It is absolutely silent, even standing directly in front of the open hood with it running, it makes almost no noise. Only the click of the clutch is audible, nothing compared to the piston R4.
The noise in my original post is completely gone. The AC works silent as can be inside the cab. Maybe because the orifice tube was installed wrong?
System cools very good, I will test it again this weekend, forecast says 88°F.

A piston compressor typically makes more noise than a scroll. Your original R4 was probably on the way out, as you mentioned, so it would have made more noise because of that. The reversed installation of the OT certainly didn't help.
Glad that you're pleased with the noise level and performance. Nice clean installation, too

[Tim]

All of our (New) R4 compressors are the scroll design.

14-20185NEW