Adding PAG oil to AC system when it's 90% new

[Kumba]

So the only parts of my AC system I'm likely NOT going to get into is the evaporator line that goes behind the engine, and maybe (hopefully) the TXV/Evaporator. I'm replacing the AC Compressor, Condenser, Receiver/Drier, and likely flushing and rebuilding the Compressor and Condenser lines.

The shop manual and the paperwork that came with the AC compressor says the total system oil capacity is 7oz. It then goes on to describe how much you add to the individual components if you replace them. Breakdown goes like this:

2oz for Receiver/Drier
1.5oz for Evaporator
2oz for Condensor
2oz for Pressure Relief Valve
2oz for Hoses

The AC compressor is pre-filled with 7oz of oil. You're supposed to drain the old compressor and then remove oil from the new one based upon how much came out of the old one. If I assume we remove the most amount of oil, that would leave 3oz left in the compressor.

If I assume the evaporator stays the same, I wind up with 11oz of oil to add to the system.

So I'm thinking I need to abandon all that noise and do it a different way. One idea is to leave however much oil in the compressor as their replacement chart for just the compressor states, and then inject the remainder of the oil while charging into the low/suction side as the compressor runs.

A second idea is to assume there's 1oz of old oil left in the evaporator, then leave 3oz in the new compressor, and put 2oz in the receiver/drier and the remaining 1oz into the condenser.

Let me know if you have any feedback for me. I still have to hook up a set of good gauges and make sure I have no other issues but I know I need a new compressor as the old one is leaking. Replacing the condenser just because I found one on wholesale closeout for $46 and it's relatively easy to get to.

 

[joegr]

Okay, first your math on the oil isn't adding up at all. Total system oil charge is 7 oz, but you suggest adding 11 oz plus whatever remains in the evaporator? I would drain the new compressor and add back 5 or 6 oz and call it good. A little over or under won't hurt.

Secondly, on the flush, do you plan to use a flush machine and nitrogen after? It's not hard to DIY flush and clean the system out, but it's nearly impossible to get the flush chemicals completely out without the machine and flowing a lot of nitrogen through. If you leave any of the flush chemical at all behind, then the compressor probably won't last very long. If you do correctly flush, it solves the oil question as it will all be removed, so in that case you would add 7 oz.

 

[Kumba]

Okay, first your math on the oil isn't adding up at all. Total system oil charge is 7 oz, but you suggest adding 11 oz plus whatever remains in the evaporator? I would drain the new compressor and add back 5 or 6 oz and call it good. A little over or under won't hurt.

That's the math per both the Shop Manual and the little pamphlet they throw in the compressor box. That's why I ask, because it DOESN'T add up. Here's the Shop Manual for reference: 2006 Lincoln LS Workshop Manual

Maybe I'm just reading it wrong, but everything references how many oz to add to the oil recovered from the collection process. That's why I decided that the shop manual was likely wrong given the amount of stuff i'm replacing, and I should just split the oil up into various parts of the system so that it equals 7oz total, or have the shop I use to charge it inject the oil into the system with the charge.

Secondly, on the flush, do you plan to use a flush machine and nitrogen after? It's not hard to DIY flush and clean the system out, but it's nearly impossible to get the flush chemicals completely out without the machine and flowing a lot of nitrogen through. If you leave any of the flush chemical at all behind, then the compressor probably won't last very long. If you do correctly flush, it solves the oil question as it will all be removed, so in that case you would add 7 oz.

I'm probably using the term Flush wrong. The only thing I'm going to be flushing/cleaning is the compressor line and the condenser line. This is mostly because I need to de-grease the things to make sure the rubber is good, especially the compressor line. That one looks like it's got 1/2" of road grime caked all over it thanks to the compressor seal leaking. The compressor, drier/receiver, and condenser are being replaced with new. The Evaporator and evap line aren't being touched other then the evap line getting new o-rings where it hooks up to the condenser line.

 

[joegr]

You are interpreting the shop manual wrong. It clearly says that the total charge is 7 oz. The other figures are estimates of how much oil could remain in those components. It is useful if only one of those things is replaced. It is not to be used if multiple components are replaced. For example, if you are only replacing the condenser, then only add 1.5 oz of oil to the oil that is already in the system.

You do not add oil to individual components of the system. All oil that you add goes into the compressor. (Be sure to rotate the compressor shaft by hand several turns to distribute the oil in the compressor.) The oil is only really needed for the compressor, the seals, and maybe the expansion valve. It's just that the nature of the thing causes it to get spread out into the other parts anyway.

Any "flushing/cleaning" that you do with anything other than nitrogen has to be completely removed somehow. This usually involves a machine that can circulate a lot of nitrogen through the line/component involved until the residue of the cleaner is completely removed. If you have no real reason to flush or if you aren't going somewhere to get the flush removed, then it would be way better if you didn't do it.

Cleaning the outside of the line is not remotely like flushing it. However, any exterior cleaning that you do must be on a completely sealed system. Don't do it while anything is disconnected.

 

[Kumba]

And this is why I double checked. Thanks Joe!