1986 Corvette R-12 to R-134a Conversion

[kenlou]

OK, using 12 volts, the clutch operates as it should.

[JohnHere]

The original information that I have for your car specifies 52 ounces net weight of R-12 and 7 fluid ounces of Mineral Oil. Of course, now we're converting to a somewhat reduced amount of R-134a, which can be addressed later. But the 7 ounces of oil (be it Mineral or PAG) is still a valid spec for your system. So you'll need to add 4 more ounces of oil someplace—PAG oil this time—either to your new R-4 compressor (if it will take all 7 ounces), or to make the process easier, introduce 4 more ounces into one of the service ports using the proper tool. The latter method will eliminate having to disassemble anything, which you don't want to do at this point. After adding the oil, you can proceed to weigh-in the refrigerant—beginning at about 80-percent of the R-12 amount—into the well-held vacuum...if you can do so at your locale's ambient temperature. If not, add maybe a 20-percent charge and wait until Spring for the rest. I don't know where he finds that info but I would like to know where.

It came from an MVAC refrigerant reference chart that I copied and filed away in my archives sometime in the late 1980's. I don't recall its source. It says: Corvette, 1985-1987, all engines, 52.0 ounces of R-12, 7.0 ounces of Mineral Oil. Your FSM differs from what I have, and I can't verify whether it's right or wrong. The 52-ounce specification (3.25 pounds) seemed about right to me, though, based on the year of your car and my experience working on R-12 systems going back to the early 1960's. If the information that I have is correct, then the shop added a little more than 50-percent of what the original specs call for, which might not be enough to start the compressor.

Do you still have an under-hood decal that shows the A/C specs? If so, always go by the information on the decal as to the amount (and type) of refrigerant and oil.

OK, using 12 volts, the clutch operates as it should.

Your testing reveals that the clutch engages and therefore is good, and the compressor probably is good as well since both are new GM parts. And because almost every other component is new and designed for R-134a (pressure switches, etc.), I would guess that the charge amount is still insufficient to run the compressor unless you have a bad circuit breaker, fuse, or open wiring someplace.

[kenlou]

Thanks. If I wanted to add another 10 ounces, how would I do that with the car not running?

[Tim]

1986 Chevrolet Corvette V8-350 5.7L (R4 Compressor)

REFRIGERANT CAPACITIES
Refrigerant Charge .................... 1.02 kg (36 oz)
Oil Charge .................... 0.17 kg (6 oz)

[kenlou]

Do you still have an under-hood decal that shows the A/C specs? If so, always go by the information on the decal as to the amount (and type) of refrigerant and oil.

No, I do not.

I have the ACDelco LTR4 compressor with clutch and the connector from the car is a 2 spade connector that can be installed either way. It has the diode atttached in the connector and I was wondering if it mattere how that connector is attached to the compressor clutch coil terminals. Does the clutch coil have a certain polarity when it comes to connecting the car's connector?

[JohnHere]

The diode that you mention allows current to flow in only one direction. As applied to MVAC systems, it prevents current from flowing in the reverse direction that the clutch coil normally "sees." In so doing, the diode stops the current spike that's induced when the clutch coil de-energizes, preventing voltage from traveling back to sensitive vehicle electronics. If I recall correctly, the polarity doesn't matter, so the connector can be plugged-in either way.

[tbirdtbird]

If you do the math, Tim's data shows charge to be 2.25 lbs, and your service center (? a brake shop) installed 1.8 lbs).

After 9 pages of diagnostics you are very close to turning the car over to an actual certified MACS shop to be finished.

We were brought a 928 Porsche which had been R12 originally, front and rear AC. These are cars where the AC didn't work well when new. (Older German cars never do).
Car had been converted to R134, and brought to us by a new owner because of poor performance. The pressures were off the wall, why the hoses didn't blow is beyond me. Evidently this was the only way the shop could get any cold out of it. After considerable diagnostics on our part we came to the conclusion the evaps were faulty. (They would blow cold only for about the first 5 min when the car was cold.)
Changing out the evaps was something we cared not to do....you do not remove the evaps from the car, you remove the car from the evaps, i.e. disassemble the entire car. We sent the car to another shop we refer to. Owner had to wait 9 months for them to get to the repair. Turned out the foam around the edges had disintegrated and clogged the fins, and internally the piping was clogged with a goulash of congealed mineral oil. The car had been converted improperly.

Your 9 pp has gone on for so long I really have no idea what has been done or even what was wrong.

[Tim]

If you do the math, Tim's data shows charge to be 2.25 lbs, and your service center (? a brake shop) installed 1.8 lbs).

The data I posted is from ALL data, OE charge.

[kenlou]

tbirdtbird

Your 9 pp has gone on for so long I really have no idea what has been done or even what was wrong.

Long story short:
I converted my 86 vette over to 134a. I replaced ALL components of the original AC syatem but the Evaporator tube/liquid line. I also installed a new parallel flow condensor.
I came here last December with questions, and with the help of JohnHere, DetroitAC, and you I was able to get the system charged with a holding charge of 25.6 oz using a digital scale and kept track of the the precise weight I put in it so that I could follow-up weighing in the rest of the refrigerant in the Spring.
Well spring has sprung and I came back for more advice on how to continue from where I left off last winter. I was convinced to take it to a shop and let them recover/evacuate/recharge. It definitely seemed like the best way to know how much of that initial holding charge is still in there.

I told the shop how much refrigerent I put in last winter and that I wanted to know how much refrigerent they evacuated so I could determine how much I lost over the winter.
There must have been some mis-communication somewhere along the line, because that didn’t happen….kinda pissed me off too.

I get a call telling me they can not get the compressor to kick on so they stopped where they were. The $$$$ can add up quick so I got it home and will see what I can find out.

They tell me that they put in 1.8 lbs of 134 along with dye….according to his chart??? I know this is wrong.

I figure it should have 36 oz of 134.

So, here I am sitting with a partially charged system with dye that could not be distributed because the compressor did not start for them.

And I have absolutely no idea how much refrigerent I lost over the winter.

So to continue the saga, I am back hoping to get more help to finish this thing.

I wanted to start with confirming that the compressor is good or not good. Using 12 volts, I confirmed that the compressor clutch operates as it should.

tbirdtbird

If the full amount is not added chances are good the comp will not run.

JohnHere

Your testing reveals that the clutch engages and therefore is good, and the compressor probably is good as well since both are new GM parts. And because almost every other component is new and designed for R-134a (pressure switches, etc.), I would guess that the charge amount is still insufficient to run the compressor unless you have a bad circuit breaker, fuse, or open wiring someplace.

So my next question:
How do I get enough refrigerent added to get the compressor running? I would like to at least get the dye circulated so that I can determine if there are any leaks.

[JohnHere]

The recurring problem, as I understand it, is that the compressor refuses to engage even after a shop charged it.

We also have four R-12 specs for this car, none of which agrees: Kenny's FSM, the shop's, mine, and Tim's. There's no under-hood decal to guide us, either. The question is, which of the specs, if any, is correct?

Kenny, it might be worth calling your local Chevrolet service department to see what they can tell you.