Green89IROC305

Hey all,

Put together my 91 Z28 with all new AC components except the evaporator core and the low side line.

the discharge line is designed for an 87 it reaches across to the driver side.

I know I need to fill the compressor with oil first curious which PAG oil I should use for the system and how much refrigerant to fill it with. Technically it originally was an R12 so I think the ratio 75 percent of R134.

Is anything else I should know before I fill it other than the obvious vacuuming it down.

Thanks

Bob88GTA

iTrader: (2)

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sofakingdom

iTrader: (1)

This is a MAJOR mistake.

Re-using the evap isn't necessarily a problem; but leaving ANTIQUE rubber parts in there, is going to come back and bite you in the privates.

Given that the lines are the part MOST LIKELY TO leak, with the only possible exception being the compressor seal, you are almost guaranteed not to be successful in your project. Replace that last couple of feet of rubber.

I'm going to assume (yeah I know) that you've already flushed out every metal part you're re-using, including the evap and any of the metal line sections, with some sort of NON-RESIDUE solvent. Lacquer thinner, MEK, acetone, denatured alcohol, or even [gasp]AC flush[/gasp]; NOT, brake parts cleaner, paint thinner, mineral spirits. Pour a bit into the part, blow it through with compressed air and a clean white rag over the other end, repeat until there is no trace of contamination left coming out onto the rag.

That said, once you've replaced the lines, use the medium weight PAG oil. It's usually given a number around 75 - 100. Not the thin 45 or 50, and not the thick 140 or whatever. Pour about 2 oz in the accumulator and about 3 into the suction port (the one the larger line attaches to) of the compressor. Turn the compressor by hand acoupla revolutions, making sure you're turning the pump itself and not just the clutch.

Evacuate to 29" or more of vacuum and hold it there for an hour, close the system and turn off the pump but leave your gauge on it, let it sit another hour, make sure it loses no more than 1" of that vacuum level.

Once you get it leak-free and cleared of all volatiles, go ahead and fill it. It should take about 4 cans of 134A. No sense in trying to get too "precise" with decimal points of the amount: your choices basically are 3 cans, 4 cans, 5 cans, etc., with a great deal of uncertainty in how empty the cans get drawn down during the process. We call that "measure with micrometer, mark with chalk, cut with axe", and it's pretty much a giant waste of effort. It's better to leave a little too much in it than not quite enough: over time, it's pretty much a certainty that refrigerant will leak OUT, rather than the atmosphere forcing more IN; therefore if you err to the side of slightly (emphasis on SLIGHTLY) overfilling it, it will pass through "ideal", whatever that is, as time goes by and a molecule here and there finds a way to escape, rather than already starting out underfilled and just getting worse. Look for a low side pressure of about 40 psi at 1800 RPM or so sitting still on a hot (85 - 90°) afternoon with the function on Max AC and the fan on High.

Green89IROC305

Thanks for the run down on the procedure.

To be clear the discharge lines are new, the only retained parts is the aluminum liquid(low side) line and the evaporator core. I retained the aluminum line becase A it's aluminum, and B, its not easy to find new.

I replaced the orifice tube, compressor, suction hoses and condenser with new parts from 4Seasons, although the condenser is Murry I believe.

I did flush out the evap core and liquid line with compressed air until it was clean, although I did not use a solvent.

The page linked in the post above says the R4 calls for PAG 150. I just want to clarify exactly which weight PAG oil to use.

Thanks.

sofakingdom

iTrader: (1)

I don't really too much care what some page on the Internet says. I go with what works. The mid-viscosity stuff works the best.

Flush with solvent. You MUST remove EVERY TRACE of the old oil. It turns to wax in the presence of 134A.

Bob88GTA

iTrader: (2)

Sorry for trying to help

sofakingdom

iTrader: (1)

You don't have to be that way Bob. There's room for disagreement in matters of opinion. I happen not to subscribe to the "if you see it on the Internet it must be true" mentality. Long decades of personal experience seem better to me, as a guide to what to do in equivalent situations in the future.

In this particular case, the mid-weight oil matches the original R-12 oil the closest, which is why I chose it originally (90s); and 100% success ever since is why I continue to use it, and to recommend it to others.