Rapid automotive A/C decompression - Does oil escape?

[Lakewood Brian]

I've read here and elsewhere that AC compressor oil does not escape significantly when an automotive A/C system leaks slowly. But what about a sudden decompression? My serpentine belt broke and spinning belt fragments took out the compressor-to-condenser line. Tore it nearly in half, instant discharge of all refrigerant. See photo. Possibly a solid clue, I can detect no oily residue, or any residue actually, where the hose failed. That seems encouraging.

I've searched the web for nearly a week and... ¯\_(ツ)_/¯
I found a couple statements here on this site that slow leaks don't cause a loss of oil. But I have read nothing about sudden decompression, especially from a hose.

 

[Nukeman7]

Rapid decompression of the sealed A/C system can result in loss of the PAG oil. However, many factors increase or decrease the likelihood of that happening. These variables include where the rupture occurred (high pressure hose or low pressure hose), was the A/C compressor engaged at the time of the occurrence, the elevation and position of the leak, amount of refrigerant in the system, etc.

If you have not cleaned the area near the rupture, your photo appears to show little to no oil loss as the cut hose and crimped coupling look very dry. The oil is typically infused with refrigerant under pressure and will effervesce (like Alka-Seltzer) for several seconds when rapidly discharged. The oily mess would be pretty obvious in the adjacent area.

 

[Lakewood Brian]

I'm chuckling that the answer (of course) is "it depends."
It's remarkable how I don't see any oily residue. I haven't cleaned that area at all. I may have gotten lucky.

 

[Fitter30]

Suction line not so much because of the vapor, liquid will carry more oil because of higher pressure. But when it was legal 60 lb charge of R22 wouldn't carry more than 1 oz. from liquid. from 30 ton recip compressor. Dumped the charge through a manifold gauges into a bucket. And no didn't have reclaim machine.

 

[Lakewood Brian]

I'm debating if the risk from not adding oil and *possibly* being a little low on oil is greater than the risk of adding the wrong oil. Figuring out what type of oil to add is all sorts of fun. The AC sticker on the bottom of the hood says "PAG 9407724" and "SAE J639". The PAG 9407724 doesn't seem to exist in the world of Google, and some speculate PAG 9407724 isn't compatible with "PAG oil." And I don't know what SAE J639 is.

Here's the AC sticker on the bottom of the hood.

 

[Jetronic]

When in doubt, add an ounce of POE, of fairly high viscosity. Withth e fluorecent marker for future use if you desire.

another option is PAO, but I'm not a big fan of that.

 

[Chris142]

If no oil came out you need to add oil as imo it didn't have enough. What kind of car?

 

[Lakewood Brian]

It's my wife's 2016 BMW X3.
The AC ran fine. It was a broken/spinning serpentine belt that tore the compressor-to-condenser high pressure hose. She's had the car ~3 weeks and I can't find a good service manual for it to save my life. Info online conflicts regarding the proper amount of oil in the system. I'm thinking 5-ish ounces (?). I'm going to call or visit the dealership early next week to see if they have a manufacture-anointed oil to add. But I expect they'll want me to drop the car off with a signed, blank check.

 

[Marcozi]

Don't go to the dealer. Find a reputable automotive AC shop. Have the shop replace the bad hose with a part from FCP Euro. Make sure the part is labeled "OE." "OE" means the part is the same thing as the part from the dealer except the "BMW logo is missing. Have the system evacuated and checked for leaks. Then a proper refill with the correct amount of oil and refrigerant.

 

[Lakewood Brian]

Whoa. Totally blown away by my BMW dealer.

• I talked to the parts counter. They sell one PAG oil for recent-ish R134a systems. In big 10 oz bottles. And the bottle doesn't identify viscosity, it just reads "PAG Oil". He speculated likely PAG-46, similar stuff to what parts stores sell. But he wasn't certain. He said he's fairly sure the other numbers on my AC sticker under the hood don't mean anything related to the oil.
• We talked about having the service dept top up the refrigerant with their magical AC recharge machine that adds oil into the refrigerant as it fills the car. I sensed a home-run in the making... could their magical machine sense when enough oil is in the system? Rich transferred me to the service dept.
• I eventually talked to a service foreman and the magical machine turns out to not be THAT magical. We talked about the sudden hose failure and lack of oil residue. He confirmed to me that there really is no way to measure how much oil is in the system, but a sudden hose failure isn't likely to leak significant oil. Just what is volatilized in the refrigerant that leaked out. If I found oily residue all over the place he'd reconsider that, but not finding any oil residue is consistent w/ his view of how the system works. He said if I brought it in they wouldn't add any oil. They'd just replace the hose and the desiccant pack, evacuate, verify the system isn't leaking, and fill as normal.

Just when I was sure the dealership was out to break me financially, they go and do something like this. <worldview blown>

Unless anyone sees a reason not to, I think I'm just going to put on a new Genuine BMW replacement for the compressor-to-condenser line, a desiccant pack, evacuate & test the system and then refill.

 

[BC1]

Did you determine what caused the belt to break?

 

[Nukeman7]

Whoa. Totally blown away by my BMW dealer.
...
Unless anyone sees a reason not to, I think I'm just going to put on a new Genuine BMW replacement for the compressor-to-condenser line, a desiccant pack, evacuate & test the system and then refill.

Be sure to check the damaged hose for any residual PAG oil of significance after you remove it. If any measurable amount can be drained out of the hose, I'd suggest replacing that volume x 1.5 for good measure. Any extra ounce won't hurt anything. I do agree with the service foreman that it PAG 46 is the standard oil for R-134a systems.

 

[Lakewood Brian]

Did you determine what caused the belt to break?

Perfect question!

I have not figured out why the belt broke. And now I'm noticing the clutch plate on the AC pulley is always engaged, even when the AC is turned off. Even when the engine is not running. I am unsure if this is how this AC compressor is supposed to work, or if this could be caused by the absence of any pressure in the AC system.

When I replaced the belt, I checked that all the pulleys spun freely and did not have play in them. So the AC pulley spun freely, but I'll bet I didn't notice the clutch plate on the front of the pulley didn't spin independently of the pulley. I replaced the belt and everything seems to be spinning nicely a full week later. I didn't hear any abnormal noise leading up to the failure. Definitely no belt squealing. And I was listening closely to the engine - we just bought the car 2-3 weeks earlier. At 130k miles & 9 years I was assuming the previous owner never changed the belt and this was the day it finally failed. But now that I can't get the clutch plate to spin by hand when the car is not running. And it spins 100% of the time when the car is running regardless of HVAC control settings.