Mineral oil/R12 Ratio variance

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
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Bottom line you can't trust the Four Seasons Chart.. refer to service manual for year and car and also look at existing AC lables..
It's not that the 4 seasons chart is flat out wrong everywhere. Most of the time they're pointing you to the underhood labels anyway. Problem is, they do have some incorrect info in some places, making you verify the chart as you use it.

On a few occasions the factory literature gets behind in any changes or even flat out typos and wrong info, but that's rare. The underhood labels won't change but don't always tell the entire story. And that's why I wonder that if you put just 6 ounces in the system, 3 in the compressor and 1 in the evap, 1 in the accumulator, and one in the condenser, for example, the CSM still wants you to put 2 more ounces into the accumlator to make up for the oil sucked into the desiccant that ain't coming out. So 8 ounces isn't really off that mark- problem is for me it doesn't tell you why they state 8 ounces on the 4 seasons chart. GM manuals sorta get around to mentioning that. There isn't a "here's what you do step by step" laid out in a GM manual. You have to read between the lines.

Additionally, the 1978 CSM discusses how new GM units come with 5.5-6.5 ounces of oil in the compressors and to drain it out before installation and then refill with 3 ounces of oil. Well, later GM compressors came without oil. Even has a tag on it that says basically it's shipped without oil and you need to add oil to it. They put just enough oil in it during assembly to keep the bearings lubed and that's it.

On mine...I started with fresh and dry components. The compressor was a new Delco unit that I emptied and added the amount of mineral oil in the service manual. Adding the amounts of mineral oil to directly to each component worked out very well for me as it has many times in the past. You can throw all of this information out when you bring 134a or different refrigerants and oils into the equation. But from my experience (35 years working in the automotive field) you cant go wrong using the GM capacities if you are dealing with an R12 system and using factory sized components.
And that's probably the best way to do it. Not going to argue with professional experience.

Thinking more about it, approx. 8 ounces of oil into a totally new system with a new accumulator is probably best to allow for the desiccant sock to absorb a couple ounces of the oil, allowing for 6 "free" oil to roam the system and keep the compressor constantly lubed, which is the main point anyway. And anytime you open the sysytem it's probably a good idea to get a new accumulator anyway because letting the desiccant absorb moisture from the air just sitting around open will saturate it. Keep in mind, check to see if it's compatible desiccant for the type of refrigerant you're using. The newer stuff claims to work with both 134 and 12 (XH7 and XH9), but the original old school GM accumulators are just for 12 (HX5). Of course, if you don't replace the accumulator, you can skip the extra 2 ounces of oil.

My thoughts are make sure there's at least 6 "free" ounces minimum with an R-4 system, but a couple ounces more ain't going to hurt it when you replace junk in the system. GM tends to imply you should anyway with new accumulators. My concern is that R-4's have no oil reservior so all the lubricant has to come from the refrigerant/oil mix as it passes through the compressor so 6 would be the absolute minimum.
 
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78Delta88

Royal Smart Person
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May 23, 2022
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This is why Mitchell DIY site is good. Has all per year/make/model. Includes access to Tech Sheets, full Schematics and some other stuff just for that year and model.

I ran across it about a couple of months ago for the 87 Merc. I only did the monthly for 19.99. Who would think parking lamps are computer controlled?? But found out why the lights didn't work and then R&R of the blend door. Whomever designed that mess needs tossed on a tank mine.

Edit: Oops forgot the link...

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