How to get right amount of oil in AC system?

cb474

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@justalubetech Thanks for your thoughts. My compressor came with only shipping oil in it, so I have to drain it. And since I have a leak in the high pressure line, which I'm replacing, I need to compensate for that. Plus whatever was in the drier, which I'm replacing. They also warn you in the instructions never to put more than half of the system spec in the compressor or in my case not more than 3oz, because too much oil in the compressor, before it has circulated through the system, can cause it to lock up when it is run for the first time. So at least in my case, in seems a little more complicated. It also seems like if I don't add extra oil somewhere else in the system, in my case I'm going to use the discharge hose, I would risk having less than spec in my system and, as others have said, too little oil is worse than too much (at least if you only go over by an oz or two).
 
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So I had the system evacuated. The technician at the AC shop said the machine pulled 1.75 oz of oil out with the evacuation. He also said that they always make sure there are 4 to 5 oz directly in the compressor, before they install it.

I explained that the spec from the Mazda service manual for the whole system is 5 oz (although I still find the wording confusing, "A/C compressor oil sealed volume (approx. quantity)" = 5.07 oz). The technician really didn't believe that was right, but basically said, do whatever you want.

He also said you never really can drain all the oil well from the old compressor to know how much was in there, so he was dubious about that method. (That being said there's shipping oil in the new compressor, so I do have to drain that all somehow.) And the technician pointed out my old compressor was leaking (in addition to the high pressure hose), which I thought might be the case when I was tring to repair the clutch, so he thought it's anyone's guess how much has leaked and what's really in there.

So I'm wondering if I should just put 5 oz in the new compressor and call it a day.
If you can find the Mazda service documentation, it’ll tell you to drain the oil from the new compressor, measure it and subtract an amount if no other parts are replaced(like the evap/condenser, dryer/desiccant sock, hoses, TXV) and pour the new amount back in or if the entire system is replaced, leave it in.

All compressors from the dealer as well as Denso brand ones and many others have the right PAG oil in them from the factory. Many techs will blindly slap them on without adjusting oil level.

If you can’t find the amount to subtract, a good guide is 1/2 ounce for major leaks and replacing the desiccant sock, and an full ounce for evaporator/condenser.
 

cb474

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@nthach Thanks. Yes, I think that's all been pretty much covered above in the thread, but I appreciate your summary of the usual advice.
 

cb474

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The amount that went out the hose is very minimal. I would drain the old compressor and let me know how much you got out. Are you changing the reciever drier too? Is it a bag or a metal cyl?


Edit: I looked at the reciever online. I would add 1 oz of oil for that. I would add 1/2 oz for the leaking line. Then measure what I got out of the compressor+ another 1/2 oz.
Well, I only got 0.7 oz out of the old compressor (I took my time and turned the clutch a lot--there was really not even a drop left coming out). The tech who evacuated the system said the machine pulled out 1.75 oz. I wonder if that really all came from the compressor?

So if I follow your advice, 1 oz for the drier, 1/2 oz for the leak, 0.7 oz for the cold compressor, 1/2 oz for good measure, and (I assume) 1.75 oz for what the machine pulled, that would mean I should put in 4.45 oz. That's pretty close to the total system spec 5.07 oz.

I suppose it's safe to assume there's at least 0.62 oz still in the condenser and the evaporator. There service manual says to add 0.8 oz when replacing the evaporator and 0.7 oz when replacing the condenser. So I guess there could still be as much as 1.5 oz in the system.

But with the leak I had, which was there for a long time, I'm still wondering if I should still go ahead an add the full 5 oz, in the interest of being sure I definitely have at least the full system spec. If I did that I guess I would risk possibly ending up with 6.5 oz in the whole system, at the most, but avoid only actually having 4.45 oz, if there's really hardly anything in the condenser and evaporator now.
 
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wtd

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Both of the lines to the drier connect on the bottom. It seems like if I pour oil in there, it's going to drain back out when I install the drier. It would be hard, I'd think, to turn it rightside up with the ports down and connect both lines quickly enough not to have oil running out.
Like Chris stated above, you can put the oil any place in the system. If you are replacing the high pressure line, put oil in it instead of the drier. The oil is going to get distributed throughout the system as it runs. Don't over think it. Get what you can out of the compressor and then maybe subtract a little amount that might be left in the evaporator and condenser if you don't replace it and then put the remaining amount in the compressor and high pressure line.

Without completely flushing the system and replacing all of the components that can't be flushed, you will have no idea how much oil is still left in the system. If the oil capacity is a little over 5 ounces, I would just put 5 ounces in it and call it good.
 

cb474

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@wtd Thanks. Yeah, that's what I did, I put the extra oil in the high pressure line. I found that suggestion already in a YouTube video. Actually, if anyone is interested, this video is probably the best thing I found on YouTube about dealing with the oil in the AC system. I guess this guy is an instructor for AC technicians or something like that. I also enjoy his slightly exasperated, I've seen it all, high school instructor type of voice.

Anyway, I probably am overthinking it. I ended up putting in 4.5 oz, as I mention in my previous post, following Chris142's suggetions for how to figure it. 3 oz in the compressor and 1.5 oz in the high pressure line. I was only able to get about 2 oz of shipping oil out of the new compressor. I hope that was all of it. I talked to someone from the AC compressor manufacturer and they said there should be about 3 oz of shipping oil in the new compressor. But the instructor in that YouTube video says that the amount of oil that ships in compressors is often very different from what the manufacturer claims and you should always drain it and put in the oil yourself.

Anyway, I hope I don't have way too much oil. But it seems like it's probably okay.

I still have to replace the drier. Dealing with the compressor and the high pressure line took me a lot longer than I thought it would. As well as dealing with the dreaded stretch tension AC belt on the Mazda 3. I'm going to try to do the drier in the morning and then go get the system recharged at the AC shop.
 
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@wtd Thanks. Yeah, that's what I did, I put the extra oil in the high pressure line. I found that suggestion already in a YouTube video. Actually, if anyone is interested, this video is probably the best thing I found on YouTube about dealing with the oil in the AC system. I guess this guy is an instructor for AC technicians or something like that. I also enjoy his slightly exasperated, I've seen it all, high school instructor type of voice.
Thanks for the YouTube link! Going through this ordeal myself when replacing parts on my Buick.
 
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@JGmazda Good luck with your repairs. Hope it goes well.
Thanks! Actually... it didn't go as planned! I had a compressor replaced (repair shop) and the results were marginal at best. (Most likely cause is the non-replacement of associated parts. (i.e. Condenser, drier, etc.) I evacuated and replaced those parts but.... (like you) have had concerns about the oil and refrigerant.

Currently... I fee the replacement compressor was damaged by crap in the lines... I'm looking to start over again... It's been a real cluster.

Let us know what happens with yours! Thanks!
 

cb474

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Well, I installed the compressor, new discharge line, and drier and then borrowed a vacuum pump and manifold gauges from Autozone yesterday and recharged the system myself. There were no leaks (I was really dreading that there would be) and everything is working great. My old compressor, with the clutch partly falling off and leaks, only blew at 65 degrees, now the system is going down to 41 degrees. It hasn't worked this well in years. I'm very excited. This is the most complicated car repair I've done. Really, I haven't done my own work on my car since my youthful days with my 1981 Celica.

Thanks so much to everyone who answered my questions and shared their thoughts and especially to Chris142 who responded here and in another thread very quickly and with very helpful insight.
 
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