Adding PAG oil to to AC Drier

[ndz]

This post replaces my old thread with misleading title: https://www.bimmerforums.com/forum/s...e-with-a-twist

My AC evaporator was leaking and it took me about two months to replace it. I'm just getting the dash back together now and will be replacing the drier shortly.

The system has been open for a long time and it was suggested that I add 25ml of PAG. My questions are:

1. Exactly what PAG oil should be used? Does the type matter?
2. Do I just pour the (25ml) of PAG oil into the new drier?

I plan to bring the car to a shop next week and ask them to pull vacuum for 30+ min to check for leaks and remove moisture before refilling with 134a. Should I have any other special instructions for them or am I missing any steps here? Thanks for the help.

[geargrinder]

Oil is always tricky... there's supposed to be a specific amount in there, in theory ideally you either:

1. use an evac machine that captures any that gets sucked out and you replenish by the same amount, using the AC machine,
or, if its a major overhaul and a bunch of parts have been replaced, you
2. drain / clean all the AC system parts (or use new ones) and put the full dose in at recharge.

Almost all reality is someplace in between, like you know you lost some extra from a pressure leak that the machine didn't recover, and you don't want to pull all the parts etc. etc. The Techs I know usually 'eyeball it'. Aka "we recovered X ml, I'm gonna shoot X+5 ml in for good measure".

I see some stuff on the innerwebz about "SAE prohibits onboard oil charge" but I've seen it on the machines myself so don't know what that's about. The SnapOn machine does it for sure.

[pshovest]

How much oil drained from the old evap?

[ndz]

Unknown amount, since I had a major evaporator leak with oil puddling on the ground and 0psi/0psi after the car would sit overnight.

Good progress today, just need to screw in the center console, radio, climate control, add/bleed coolant, and the replace the drier. I also replaced the cowl and the piece beneath it under the hood. Hopefully Monday I'll have an A/C shop vacuum and fill.

So do I still add the PAG to the drier or does an A/C shop add it to the system? If they pull vacuum, does that remove any PAG oil that I added?

[pshovest]

Tell the shop what happened and have them determine qty to add. Evacuating an empty system system doesn't remove oil.

[JimLev]

Might be a good idea to remove the belt on the compressor just in case.
It shoudn't run with no charge but you never know.

[cnn]

When you Evap went south, your AC compressor is not far behind. My AC compressor made a lot of noise at 160K.
I replaced it and wrote all info in the DIY below.

- The only place that needs oil is the compressor. During the operation of the AC compressor, oil is distributed throughout the system, which is not under anyone's control. In other words, oil is only needed inside the compressor, anywhere else, it is a nuisance. Engineers calculate system PAG oil capacity to be sure the compressor always have enough oil.

- Consider replacing the AC Compressor to save you from repeating this job later (Evac and Recharge is costly).
If you replace the compressor, then add a bit extra for the Evap (maybe 2 extra oz):

http://www.underhoodservice.com/ac-o...essor-failure/


DIY: 1998 BMW 528i 160K Replacing AC Compressor
http://www.bimmerfest.com/forums/sho...d.php?t=924320

[geargrinder]

Tell the shop what happened and have them determine qty to add. Evacuating an empty system system doesn't remove oil.

Yeah right. Oh wait i mean not at all right.

1. Nobody can magically determine what oil did or didn't leave the system. As I said before it's typically a best guess "expert estimate" in best of cases, unless the system is entirely new. Anybody who claims otherwise is bullcrappin.
2. And yes evac may in fact pull a little oil out - which is easily collected and measured by the modern tech machines, but is invisibly lost in rudimentary gear. Hence the fudge factor / can't calculate angle.

- - - Updated - - -

oil is distributed throughout the system, which is not under anyone's control. In other words, oil is only needed inside the compressor, anywhere else, it is a nuisance. Engineers calculate system PAG oil capacity to be sure the compressor always have enough oil.

All this ^^^

[vinyldude]

PAG oil has a few different viscosities, and which one to use is compressor specific. I think most BMW (Denso) compressors need PAG46 oil but you may need to check that.

Like others have said, since you had a leak that may have caused oil loss, nobody knows how much you have it left there in the system. If you had not lost any oil, they would recommend to add about 1.5 oz (assuming 4 oz total need for oil) or about 1/3 of the total amount when replacing an evaporator.

So you could add about that much (plus some) if you wanted to roll the dice. A little bit more oil is better than not quite enough. If you wanted to do it properly (but which is trouble in your situation), you would detach all AC components, pour all old oil out, and flush the lines clean. Then add the required total amount of oil to the compressor before putting everything back together. (Then vacuum for a good amount of time to get any moisture out, followed by a new R134 fill.)

[ndz]

Thanks for the suggestions and links. The compressor works fine and the car only has 115k miles so I don't plan to replace that until I have to. So far advice has been to add somewhere between 25-50ml so I'll probably add somewhere in the middle straight into the drier and roll the dice.

Any other tips or warnings are greatly appreciated.

[pshovest]

Yeah right. Oh wait i mean not at all right.....

1. Nobody can magically determine what oil did or didn't leave the system. As I said before it's typically a best guess "expert estimate" in best of cases, unless the system is entirely new. Anybody who claims otherwise is bullcrappin.
2. And yes evac may in fact pull a little oil out - which is easily collected and measured by the modern tech machines, but is invisibly lost in rudimentary gear. Hence the fudge factor / can't calculate angle...

I've serviced my AC's for 40 years. Evacuating an empty system does not remove an appreciable amount of oil. On the other hand removing refrigerant from a system that has a full charge removes oil as the oil is entrained by the flashing refrigerant.......and yes, the best expert at guessing is the shop that changes AC components regularly, not the internet experts in this discussion. There is no substitute for experience.

[djb2]

The shop is still just guessing. The location and rate of the leak will affect how much oil leaks out with the refrigerant.

In old automotive A/C systems the oil intentionally flowed through the system. It was the oil coating on the walls of the rubber hoses and at the joints that reduced the diffusion of refrigerant. R12 was good at moving mineral oil, so this wasn't a problem.

R134a isn't as good at moving lubricants. With barrier hoses and R134a the goal is to minimize the oil leaving the compressor, and design to optimize the return of the oil that tends to puddle in the evaporator by keeping the flow velocity high. If the leak happened to be in a stagnant area, it could have pushed out a good proportion of the oil. If not, minimal oil would be removed. Even a few ml of sprayed oil wets a large area, so it's tough to judge how much came out. A shop is going to err on the side of overfilling oil.

It sounds as if you are doing most of the work yourself. Have you considered refilling yourself? Many chain auto parts stores have tool loaner programs that include vacuum pumps and gauge sets. You'll generally only need to purchase a fill hose and can tap/adapter.

[geargrinder]

I've serviced my AC's for 40 years. Evacuating an empty system does not remove an appreciable amount of oil. On the other hand removing refrigerant from a system that has a full charge removes oil as the oil is entrained by the flashing refrigerant.......and yes, the best expert at guessing is the shop that changes AC components regularly, not the internet experts in this discussion. There is no substitute for experience.

Thanks for making our point again and clarifying the misleading errors of your previous post.

[ndz]

It sounds as if you are doing most of the work yourself. Have you considered refilling yourself? Many chain auto parts stores have tool loaner programs that include vacuum pumps and gauge sets. You'll generally only need to purchase a fill hose and can tap/adapter.

I have a harbor freight gauge set but no vacuum pump. For the cost of a fill, I could probably get a pump.... Maybe I'll go for it.

The car is almost back together, just the console and radio components are left. Then the Drier which I'm still on the fence about filling with oil and how much to add.

[djb2]

Remember, don't open the drier until the last second. Do a practice round of installing the old drier and evacuating the system so that you work out any quirks and start with a mostly-dry system.

Remember, you DIY project is not a high-turnover shop environment. You don't need to do a just-barely-OK repair and move onto the next job. Hook the vacuum pump up for the recommended time, let it sit for an hour, pump it down again and repeat. You can dry the system better with a cheap single stage vacuum pump and lots of time than an expensive multi-stage pump with the minimum time.

The desiccant in the drier can absorb between 20 and 40 drops of water, but don't count on that. Start with a dry system and leave the drying capacity for water molecules that are bound to the oil, polymers or corrosion in the system.

[pshovest]

Thanks for making our point again and clarifying the misleading errors of your previous post.

There are no errors in my post, but thank you for again demonstrating the arrogance we've come to expect from your posts.

[pshovest]

The vacuum pump will easily pay for itself several times over as you make this and future AC repairs. Don't forget to drain oil from the old dryer.

[geargrinder]

There are no errors in my post,

Right. None except in stating flatly that oil can't be lost from the system from evac'ing (oh wait... Now you have some conditions and clarifications... Riiiiiiiggght)

but thank you for again demonstrating the hilarious humor we've come to expect from your posts.

No prob my friend! I am here to amuse!

[tptrsn]

I've recharged a few of my systems with good results so far. A couple with a vacuum pump rented from Autozone and my 540 with a supposedly higher capacity vacuum pump I bought.

My supposition was that more oil in the system would tend to lubricate better than less would, and that the only negative from having more than the optimum amount of oil in the system would be the potential loss of cooling capacity of the system. Therefore, if the system cools like a champ, it's probably ok. So I looked at the recommendations for how much oil to add back into the system after changing to "X" new part, and erred on the high side.

Fingers crossed, but so far all of them have cooled fantastically, so I guess it's all good to this point.

[ndz]

The vacuum pump will easily pay for itself several times over as you make this and future AC repairs. Don't forget to drain oil from the old dryer.

I'm picking up a pump today. Why would I need to drain the oil from the old drier if I'm replacing it?

[djb2]

I'm picking up a pump today. Why would I need to drain the oil from the old drier if I'm replacing it?

They might be suggesting to measure the quantity of old oil. But the receiver/drier is also the filter for the system. You won't get a good estimate of how much oil is retained in the filter media.

If quite a bit of oil pour out, the only conclusion is that the system was previously overfilled with oil. Which doesn't leave you any more informed about how much to add.

[pshovest]

I'm picking up a pump today. Why would I need to drain the oil from the old drier if I'm replacing it?

I applaud your determination to tackle the difficult evap replacement and ecav/charge the system. I've always found AC work to be very satisfying. No need to drain the drier, there's a better approach. Looks like system holds 5-6 oz. In lieu of guessing about how much oil to add, consider removing compressor, draining the oil overnight and then adding a full charge. This also lets you check the oil for color and particulates. Do this and you'll never wonder if oil charge is correct. With the compressor and drier out, out you should blow thru the condenser to push out any remaining oil.

[ndz]

Just an update. I added 30ml of PAG oil to the new drier, vacuumed 30min, left the gauges overnight, vacuumed again, and added 1.6lb of 134a. So far so good but I won't have a true test until it warms up outside.

Thanks to all for the advice. Merlot is back:

merlot2018.jpg

[ndz]

Cold AC all summer. Success. Thanks again everyone.

[creative gunner]

hi, which PAG oil did you use? 46 or 100?

thanks