A/C recommendations for the MB vehicles - Page 31 - PeachParts Mercedes-Benz Forum

Squiggle Dog · #**451** 07-24-2018, 03:29 PM

Quote:

Originally Posted by ROLLGUY

Something is wrong with that. I see 8oz bottles at all the stores for around $12.

I couldn't find double end-capped PAG100 at any local stores. AutoZone would have had to order it.

funola · #**452** 07-24-2018, 04:42 PM

I have been running Behr Hella PAO 68 oil in my 85 300D with a stock AC system with a remanufactured R4 for 2 summers now with no issues.

https://www.autoserviceworld.com/carsmagazine/ac-compressor-oil/

ROLLGUY · #**453** 07-24-2018, 08:44 PM

I question why you don't want to run Ester oil? Although I have not tried it, funola and others suggest PAO 68. For me, any PAG would be at the bottom of my list. I personally would run PAO 68 before running PAG.

ROLLGUY · #**454** 07-24-2018, 09:09 PM

Admittedly I don't know much about PAG oils, but Mr. Google divulged some information:

"The double end capped PAG is a chemical structure term. PAG lubricant is an ether based polymer made from ethylene oxide and propylene oxide. The polymer can be started (initiated) from water or an alcohol. If it is started from water and no further post polymerization treatment is performed, you will make a PAG diol (no end capping at all, both ends of the polymer are alcohols). The diols are less stable and take up more water than other types of PAG.

If you start the PAG polymer from an alcohol (butanol for example) and do no post polymerization processing, you will get a single end capped PAG (one end is the terminal alcohol and one is the butane / alkyl end of the butanol initiator). The GM PAG is single end capped.

If you take a single end capped PAG and react it with methyl chloride, you can 'cap' the terminal alcohol and make a double end capped PAG, one with no alcohol groups on the ends of the polymer chain. This is the most stable and least water uptaking PAG available. It is also the most expensive due to the extra processing to cap the terminal alcohol group. The Ford PAG is double end capped. "

My question is- How do you know what brand of PAG is SEC or DEC?

Squiggle Dog · #**455** 07-25-2018, 11:02 AM

After several hours (actually, days) of exhaustive research regarding refrigerant oils, this is the gist of what I found:

1. Mineral oil works fine for R-12, but isn't a great oil, reacts horribly to any other oils, and isn't compatible with R-134a.

2. Ester oil is compatible with R-12 and R-134a, but isn't that great of an oil and there can be problems with acid formation and water absorption. The upside is that it mixes with mineral oil to some extent, so it's often used in R-12 to R-134a conversions.

3. PAO oil is universal and is supposed to work with both R-12 and R-134a, but supposedly there are lots of potential problems with using it and it doesn't mix with PAG oil, but the upside is that it doesn't absorb moisture like ester oil.

4. Single end-capped PAG oil seems to be superior to the above oils, but is always listed as "not compatible with R-12". Supposedly it chemically reacts with R-12 and decomposes as it's not stable like the double end-capped variant.

5. Double end-capped PAG oil seems to be the best possible oil and is compatible with R-12 and R-134a. As long as the system has no traces of other types of oil, it seems to be superior. The downside is it's very expensive.

I just wasn't impressed with anything other than double end-capped PAG after all the things I read about the other oils.

If the bottle of PAG doesn't advertise in big, bold letters that it's double end-capped, then it's likely not.

Diseasel300 · #**456** 07-25-2018, 11:13 AM

It's easy to overthink things when you're guessing. If you have even the faintest intent of ever running R12, use PAO or POE (Ester) oil and stop overthinking it. If the system is sealed and you have a proper vacuum pulled, there are no downsides to either. Ester oil (POE) is the standard oil used on all modern HVAC installations, so it's clearly "good enough".

Squiggle Dog · #**457** 07-25-2018, 11:43 AM

Quote:

Originally Posted by Diseasel300

It's easy to overthink things when you're guessing. If you have even the faintest intent of ever running R12, use PAO or POE (Ester) oil and stop overthinking it. If the system is sealed and you have a proper vacuum pulled, there are no downsides to either. Ester oil (POE) is the standard oil used on all modern HVAC installations, so it's clearly "good enough".

Well, I also use Amsoil. I tend to be an overachiever, but I like to do things the best they can be done. I'm sure the other oils would be "good enough" but where I live, this system is going to take a beating.

Squiggle Dog · #**458** 07-26-2018, 04:00 AM

Quote:

Originally Posted by ROLLGUY

Normally the complete system will require about 8oz total of oil.

The factory service manual states 170cc/5.75 oz of oil for a W116 300SD. As I understand it, this is total system capacity, that the 5.75 oz of oil will mix in the system and is why when the compressor is replaced, only a part of that oil will be in there, with the rest in other components at the specified quantities. But, in a new system, the entire 5.75 oz of oil should be filled and split between the compressor and drier.

I got the DEC PAG100 oil. I was sent 32 oz of it even though the auction was for 12 oz. Not bad for $30 and free shipping for double end-capped, though it's more than I will need.

I am using a Sanden 508 compressor and I am assuming that the factory spec of 5.75 oz of oil to the 2.65 lbs of R-12 is a fine ratio for the compressor even though the original compressor was a Delco R4? Sanden wants the oil to refrigerant ratio to be within 3% and 8%, and I think this comes out to just above 7%.

But then I was reading somewhere that Sanden compressors aren't designed to run on less than 7 oz of oil--but this makes no sense to me, because isn't the oil to refrigerant ratio what matters? 7 oz of oil is much higher than the system capacity and it would likely saturate the mixture too much and reduce efficiency. Then again, in a very large system it wouldn't be enough oil. I would think that the ratio matters more than just an arbitrary filling volume.

I was under the impression that the W123 and W126 diesels use 6 oz of oil, slightly more than the W116 diesel. 8 oz seems like it would be too much oil, unless using a Sanden compressor somehow changes that. It seems like I can never just install anything... I always get these questions that I end up spending hours trying to figure out and then nothing gets done.

Diseasel300 · #**459** 07-26-2018, 09:53 AM

The Sanden has an oil sump. The R4 didn't. You have to account for that. The Denso compressors on the later systems all use roughly 8oz oil.

ROLLGUY · #**460** 07-26-2018, 10:34 AM

Yes, since the Sanden has an oil sump, most of that oil stays in there. The system needs additional oil to circulate with the refrigerant, and about 2oz works just fine. Even with a P.F. condenser, the W116 system should have more capacity than a W123. Everything is a little larger. I think the new 7 cyl Sandens take 200cc of oil, but your SD508 may have less in it from the factory. Either way, 6oz in the compressor, and 2oz in the rest of the system should be just right.

Squiggle Dog · #**461** 07-26-2018, 11:34 AM

Post #10 and #13 claim the Sanden 508s have no oil sump? https://www.jalopyjournal.com/forum/threads/aftermarket-a-c-question-re-clocking-a-sanden-compressor.505164/

This post seems to claim the same thing: https://www.s10forum.com/forum/f125/you-cant-stop-sanden-oil-blowby-320994/

My understanding was that the Sandens don't have a sump. It makes sense that if there's more space in the Sanden compressor than the R4, that more oil would be needed, but do we know exactly what the difference is, or is it an educated guess?

Klima Design Works says to use 6 oz of oil in a W123 or W126 that has a Sanden conversion; 5 oz of oil in the compressor, and 1 oz of oil in the drier. That's just a little more than what the book says my car takes (5.75 oz). I don't know if they are going off of actual research or just using data from the service manuals.

I drained the compressor, added DEC PAG100, let that drain for a while, and then added 5 oz of oil to the compressor and .75 oz of oil to the drier. If I need more, I can add more later. I haven't been able to find any hard facts on if going from a Delco R4 to a Sanden 508 changes the oil capacity of the system at all. The same with a parallel-flow condenser that is one inch narrower than the factory one. So many variables come into play and it's never easy.

Maxbumpo · #**462** 08-30-2018, 06:31 PM

I'm looking at what would be required to retrofit my '87 wagon (124.193) with R12, and a question in my mind is the expansion valve. When I rescued this car the AC didn't work, and it had already been converted to R134A. I fixed all the issues but R134A just isn't working for me, and now I've got a slow leak in the evaporator.

I'm going to try to fix that leak in the evaporator with ClipLight sealer. Once that's fixed, and proven so using a test refrigerant, I'd like to go back to R12.

I've found a vendor that sells two different expansion valves for 124 cars, one says Tonnage = 2.0 and Superheat = 5.5, vs the other expansion valve with Tonnage = 1.5 and Superheat = 11. Vendor says both are for R134A, the second valve with Superheat = 11 is clearly marked on the side for R134A but the first has no markings that I can decipher. Is the first valve maybe NOS and meant for R12?

Diseasel300 · #**463** 08-30-2018, 06:42 PM

From what I was able to work out when retrofitting the SDL, the expansion valves are ALL set up for 134a nowadays. R12 was phased out in 1993 and has been strongly deprecated since.

I run the 2.0 Ton TXV in the SDL and I can assure you that even in the 100+ heat we've had here all summer long, it never struggled to keep me comfortable in the car. If anything, it's a bit TOO cold on the highway, it's not uncommon to wind up with the temp wheel set around 24˚ on the highway on a 98˚ day to keep from chattering teeth in the cabin.

The key to having frosty cold A/C is to ignore the charge weight. Weigh in the 80% charge of 134a, then charge by pressure and monitor center vent temp. Keep adding until it stops dropping. You'll wind up somewhere around 87-90% charge weight and an A/C that doesn't disappoint. I'm sure the armchair experts will weigh in at any point, but a 40˚ vent temp with max fan on a 100˚ day is satisfying enough for me.

Maxbumpo · #**464** 08-30-2018, 08:56 PM

Diseasel, is your 2 ton txv original or a new valve? You started your post with "retrofitting" which I thought meant going back to R12, but you end your post with R134a. Sounds like you're very happy with R134a.

I'm simply trying to decide which valve is better for R12. Probably wishful thinking that I've found a NOS R12 valve.

Diseasel300 · #**465** 08-30-2018, 09:30 PM

I originally charged with R12 when I rebuilt the system in 2017. Unfortunately the expansion valve jammed wide open and needed replaced about a month or so later. The new valve (ordered from Pelican) is 134a rated. I was still planning on charging with R12 until the valve failed on the jug I was using (still hanging around from the 80s). Still have ~10 pounds of R12 in a can I can't get out, so I charged with 134a. The system works well enough that I don't feel the need to evacuate and recharge with R12, this summer was a real test for it and it did just fine even without window tint (which I plan on having installed before next summer). I run POE oil in my system which is compatible with both R12 and R134a so I can switch if I ever feel like it for some reason later on, though it's doubtful that'll ever happen.

The keys to having 134a work satisfactorily are to use the right expansion valve rated for R134a (the orifice is different and the powerhead is set up for a different pressure differential), having a proper refrigerant charge (which may not be the "ideal" weight for conversion), having the engine and Aux fans working properly (good fan clutch), and having the recirculation flaps working.

The last item is probably one of the most important - the "long stroke" recirculation door is the most important. If it doesn't close, you're sucking in 20-100% outside air depending on what else is still working in the flap system. The big clue that the recirculation door is not working properly is a rapid rise in vent temp when going from moving to idle after the cabin has had time to pull down (at least 5 minutes with the vehicle moving). I intermittently had this issue in my car that I finally solved by resoldering the vacuum switchover valve block that controls the flaps (a known weak point in the 124 and Gen II 126 cars).

The troubleshooting chart in the FSM says that the vent temp should remain roughly 5˚ with the moving vehicle vent temp. I've found this to hold true in my own car. If I'm getting 42˚ at the vent when moving, I'll hold 47-50˚ depending on ambient conditions at idle. When my recirculation flap was failing to close, I'd get 46-48˚ when moving at 45mph or better, but in 30mph traffic, I'd be low 50s, and idle would shoot up quickly to ~60-62˚. On a really hot day (100˚+) it just never would seem to catch up when the flap acted up. With the flap working properly, it'll pull the cabin down comfortably and be blowing in the mid 40s in ~5 mins of driving after being parked in the sun all day. Pretty decent system when working correctly.

Hopefully that's helpful.