Questions on swapping my VA compressor & re-charging

I swapped my bare aluminum v-belt Sanden compressor for a black 8-rib one from CVF last fall and I'm just now getting around to charging it. CVF said it came with 6.75oz of PAG 100 oil inside. VintageAir takes 28.8oz (1.8lbs) of R134A. I'll be renting the equipment from my local auto parts store to properly pull vacuum on the system and charge it, and buying the cans of R134A from them.

My question; it sounds like I need to add no oil to the system and I can just use straight R134A. Is that right, or will pulling the vacuum on the system for all that time remove some of the oil? I'm not sure if as the moisture sublimates of any oil would be drawn out by the suction or if I'll be good.

Also, is there a chance of having too much oil now with what's already leftover in my system combined with the charge of the new compressor? Or is that not a great concern?


It sounds like everything will balance out ok in the end but I just wanted to check with the experts on here.

Thanks!

Deleted. An expert will hopefully respond.

Don

Is the system currently 134a?

Typical procedure is to drain oil from existing compressor and put that much in the new compressor. If converting from R12 to 134a, keep the full PAG charge- the mineral oil is not miscible with 134a so is considered kind of inert

Yeah, VA uses R134A so no R12 conversion going on here.

So I need to drain the oil out of my VA compressor and measure it? Then drain the oil from the CVF compressor and put back in the same amount that was in the VA one?

Quote:

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Originally Posted by anguilla1980

Yeah, VA uses R134A so no R12 conversion going on here.

So I need to drain the oil out of my VA compressor and measure it? Then drain the oil from the CVF compressor and put back in the same amount that was in the VA one?

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It would make more sense to flush the system and then use the new compressor with the correct oil charge imho....

Not an expert...

Don

Gotcha, I hadn't thought of that. I'll have to check and see if the rental gear is capable of that.

Once you open the system you should also replace the drier.

Don

I had thought of that but I had it open for literally 10-15 seconds as I swapped the hose connections as fast as I could to avoid excess moisture getting into the system. This time I'll just pull a vacuum on it for a good half hour and I'll call it good. Next service I'll replace the drier. Might not be the best way, but I don't want this to turn into a larger project. Thanks for the mention tho.

Quote:

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Originally Posted by anguilla1980

Yeah, VA uses R134A so no R12 conversion going on here.

So I need to drain the oil out of my VA compressor and measure it? Then drain the oil from the CVF compressor and put back in the same amount that was in the VA one?

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If you're not flushing, drain the oil from the VA pump, and compare it to the compressor label. Drain the CVF pump and replace the oil less the difference between VA measured and label values. You are determining the amount of oil still resident in the system, and removing that from the CVF requirement.

Or not. The downside from too high an oil charge is slightly reduced performance