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Adding Lubricating Oil when Charging A/C?

I had to replace an O’Ring on my AC, so the system was open to the air. I am going to do an evac to get the air/moisture out and then do a complete recharge. When I recharge do I need all my cans to have oil plus the R134 refrigerant or Do I need only one of the cans to have the oil/refrigerant mixture (i.e the rest having only R134)? I don’t want to under/over lubricate the system.

I would use the R134 refrigerant that has the oil already in it.

All cans or just the first can?

Well, the last time I bought some at Walmart, there were none available without the oil. You should read the label to confirm, but using all the cans of refrigerant with oil in them should give you the right amount of oil.

I know some have oil and some don’t. My concern was in adding too much oil into the system (i.e using all the cans with lubricant).

My first instinct is to say to just have an AC shop do it. AC systems are tricky and not always safe to work on unless you really know what you are doing.

But that’s obviously up to you. If you are going to do it, I’m sure that there is an actual spec for how much oil the system is supposed to have. I would find out what that spec is and follow it. There are also different kinds of oil, so you should check that spec too.

I know your concern, and the cans of R134 that have oil in them already, have the right amount. There should be no need to mix and match. Again, reading the label should confirm this and address your concerns.

The only way to add too much oil is to do it manually, and trying to mix and match will probably leave the system without enough oil.

You need to get a idea on how much was lost due to the leak and measure how much comes out upon recovery (probably very little both times). It sounds to me like you are setting yourself to add to much oil.

Let me edit, you need to note how much came out upon recovery. Did you recover or was it all gone when you went to fix the O’ring.

That was my thought as well. I was thinking using 1 can with oil and then the other 2 without. I don’t think I could ever determine how much I lost from the leak. I know when I replaced the O’Ring, nothing came out. I can’t imagine I lost much. I figured I would be safer adding 1 can with lube than no cans with lube. Thoughts?

Didn’t you already plan to “evac” the system? Wouldn’t that get all the old oil out? Why would there still be oil left when all the refrigerant was allowed to escape? Wasn’t the oil mixed with the old refrigerant that escaped?

Evacuating an AC system only removes air/moisture from the system. None of the oil.

For a slow leak at an O-ring, figure that an ounce of oil was lost. So use one can of refrigerant with oil, and the rest without oil.


Evacing the system, doesn’t remove the oil, it only removes the gas (i.e putting the system into a vacuum will remove any air and boil off any moisture). There is still oil in the compressor and other moving parts. I may not have lost any oil or a minimal amount, which I guess is why I’m asking the question about the adding of oil. If my assumptions are wrong I need to know that too, but I’m fairly confident about them.

Thanks for confirming my assumptions.