W123 Air Conditioning - PeachParts Mercedes-Benz Forum

1983/300CD · #1 08-06-2022, 04:21 PM

A while ago, the compressor started grinding out a green refrigerant. I took it to the shop and had them vacuum out the old R134, and I bought a new compressor, drier, pressure switch, and expansion valve. I am a complete novice to AC repair, but I just got a set of manifold gauges, so I'm ready to do some damage. I have a few questions first, though.

1. Where is the expansion valve? I see a hose diving under the battery tray. Is it under the dash?

2. Does a can of "flush" remove all the oil? The new compressor is shipped filled with oil. Do I drain it? What type of oil do I use to refill and how much? I've read it's best to add oil at different points throughout the system. Any suggestions where?

3. How does 2.6 lbs of R12 translate into R134a?

Any guidance would be greatly appreciated.

Shern · #2 08-06-2022, 07:58 PM

Everything you need (and more) can be found by searching the archives.

1.) DIY on this very site.

2.) there are countless AC threads but one in particular (VSTech and leathermang) has just about everything you’ll ever need to know. Great reading.

3.) plenty of charts online

Good luck!

1983/300CD · #3 08-06-2022, 08:36 PM

Yeah, you're no help at all but I get it. I did a bit of reading and it seems the DG page has most of the information I need.

1. Expansion valve is indeed under the dash.

2. The flush will remove the old oil from the system. I am not going to track down nitrogen or R22, so I will blow it out with air, then apply vacuum. Still not sure what oil to use with R134a, but I can read the bottle.

3. 2.09 lbs.

Thanks

shadetreemechan · #4 08-06-2022, 09:59 PM

I use ester oil because it can mix with whatever was in there before in case you don't get it all the way out.
The compressor likely came with PAG. It works well too, but I think may have a compatibility issue with another oil.
As Shern says, search is your friend. Search in google for responses within this site, rather than using the search on the site. You will get better results.

vstech · #5 08-07-2022, 01:52 AM

Certainly search include my name, and leathermang several of my threads go very in depth on ac procedures.

JHZR2 · #6 08-08-2022, 11:02 AM

I think it’s great if you’re learning, but some of the questions makes me wonder if you should be working on AC yet. Not that you can’t, but rather that you have more reading to do.

Kudos on extracting the refrigerant properly.

Expansion valve can be seen in my thread:

https://www.peachparts.com/shopforum/diesel-discussion/405859-leaking-expansion-valve.html

Green oil is probably Uv dyed. I’d recommend you use a UV light to see what will be leaking. Now is the time to change as many o rings as you can.

R-134 doesn’t work truly great in these cars. R-12 is available, and the propane blends work well too. I used thst when chasing leaks, and the charge is still in there and functional three years later..

1983/300CD · #7 08-08-2022, 09:21 PM

Every o-ring is brittle and decomposing to dust. I am guessing they are all original.
I watched a video of a guy who magically took apart his old expansion valve and drilled out the smaller of the two passageways so that they are both always open. That is supposed to let you flush the whole system from the front of the car. Will this now flush the whole inside including evaporator? It's recommended to flush the evaporator backwards, so the plan is to put flush/air into the opening at the compressor, and see the return at the drier connection.

I spent the morning chasing down oil for the loaner vacuum pump and oil for the friend's loaner compressor. Hopefully, I can get some components cleaned out tomorrow.
I don't think there's anything too complicated here. As long as things are not put back together before they're ready, it's not a big deal.

h3ffe · #8 08-09-2022, 01:59 AM

Quote:

Originally Posted by 1983/300CD

Yeah, you're no help at all but I get it. I did a bit of reading and it seems the DG page has most of the information I need.

1. Expansion valve is indeed under the dash.

2. The flush will remove the old oil from the system. I am not going to track down nitrogen or R22, so I will blow it out with air, then apply vacuum. Still not sure what oil to use with R134a, but I can read the bottle.

3. 2.09 lbs.

Thanks

Sounds like you need to do some more reading. “Blowing the system out with air” will do nothing except introduce further contaminants.

Carefully look at the thread Shern suggested.

1983/300CD · #9 08-09-2022, 03:56 AM

Will compressed air remove the flush?
Will pulling a vacuum on the system overnight remove the air and moisture?
Another $50 just to fill the parts with something to remove seems wasteful.
They don't fill new parts with a proprietary gas before shipping. Seems the important thing is to get everything clean. The gas can be eliminated.

...But if I give it a few more days with the car up, it will probably bug me into getting some N from the gas store.
Just not sold on how necessary it is.

Autozone lends a flush kit including a bottle to be hooked up to shop air. I suppose that would be drier than this compressor, but air always has moisture. Still, a good long vacuum should remove it, I would think.

I don't have access to the MBACFSM, but I have read that in it, it instructs you to flush the evaporator in reverse direction of normal flow. Does that go for the condenser up front as well? Sorry, couldn't find that in the thread.

h3ffe · #10 08-09-2022, 07:44 PM

1. Compressed air is used in conjunction with AC flush to move the flush solution around the system.

2. Pulling a vacuum removes moisture from the system. If it has been open to ambient air for more than a minute or two, you'll need to vacuum down for a long time to get below 500 microns (commercial HVAC standard for a "dry" system). A really dry system will be down below 100 microns. The rental vac pumps from Harbor Freight or similar do not have the capacity to vac a system down that has been open for some time. You need a much stronger vac pump and fresh vac pump oil to remove all the moisture and contaminants. You also want to use a Schrader valve coring tool to remove the valves without introducing further moisture. This increases the orifice size and decreases the required vac time.

3. For bonus points, boil the oil until it too is dry before it goes in the system - meaning put the correct amount of oil in a cup inside of a sealed container with a vac port on top and vac it down below 500 microns. This will further reduce vac time.

4. Nitrogen is not proprietary - it is one of the most common elements on Earth. No, manufacturers of AC components don't ship them sealed with nitrogen, because the expectation is a professional tech will pressure test the assembled system and then vac down. Pressure testing with nitrogen or similar inert gas is the only way to ensure your system is leak free. A vacuum is not a leak test.

5. A good shop air system has runs in it with valves (think a trumpet or trombone spit valve) to collect the moisture and ensure the air coming out of the nozzle is as dry as possible.

6. Auto AC is not specific to W123 or Mercedes. Branch out and dig into some other reading materials and Youtube videos made by HVAC professionals to get to know your way around an AC system before you potentially ruin expensive parts.

7. If you don't ensure a leak free and dry system, you won't necessarily have immediate compressor failure, but your system will never operate as it should. Having an incorrect mixture of refrigerant and oil will damage your compressor. Think running your car low on oil. It will run for some time, causing internal damage, and eventually seize. You may not have a "problem" (i.e. noticable in vent temps) for a few months, half a year, or a few years, but you'll damage and eventually destroy the compressor. If it blows, you'll have metal shavings all throughout the system and a big problem on your hands. Many auto shops that aren't HVAC specialists simply use a Robinair or similar type of machine that will get you on the road, but wont give you optimal performance or as long lasting of a system. That's why you see vehicle owners fighting AC, with compressor replacement after compressor replacement.

8. Yes, flush every component in the reverse direction of normal flow.

9. R134a will cause higher head pressures than R12. Look into the propane blends like R12a. Shern's recent AC thread is a good read and follows his (successful) process.

10. Analog AC gauges will not tell you how deep the vacuum is. They will peg at 29 Hg of mercury, but a digital micrometer will show you that an analog gauge can be pegged at 29 Hg but still be at 10k+ microns. Not dry at all.

Good luck, and get to reading.

ykobayashi · #11 08-10-2022, 06:55 AM

Quote:

Originally Posted by h3ffe

3. For bonus points, boil the oil until it too is dry before it goes in the system.

Thanks for this tip. I have all these half filled bottles of PAG oil from various projects I’ve saved but don’t use because I know they’re no longer dry.

1983/300CD · #12 08-10-2022, 07:38 PM

I know the oil is hygroscopic, but the bottle is sealed.

I decided to get some Nitrogen so that I can do a pressure test when it's all put back together. I've removed the compressor, drier, and drilled out the expansion valve's smaller hole. After another (backwards) flush with solvent through the evaporator and condenser, I'll remove the hoses and make sure they're all clean and dry. Any objections to using Nylog blue on the fittings and o-rings at reassembly?

I've read 8-10 ounces is a full charge of oil for this system. I've also seen a video explaining that a system with an expansion valve should get half of the oil put in at the evaporator, but I'm not 100% sure on how to make that happen. The hose after the drier goes uphill. Do I inject oil into the evaporator before I install the new expansion valve?

I saw a guy use a vacuum pump on the yellow manifold line to draw a couple of ounces of oil into the high side, but as I understand it, you want to add oil after the drier.

I'm reading, but there's a lot to sift through. I'm going with this compressor and coolant because that is what I have and I know these compressors don't live forever. Maybe next time, I'll get a Sanden and parallel flow condenser, but it's getting this setup one more time.

And yeah, sorry, I meant preparational. I guess.

1983/300CD · #13 08-13-2022, 10:06 AM

As far as I can tell, a safe charge of oil would be to add four ounces into the compressor (spun 15 times), two into the condenser, and two into the drier, totaling eight ounces.

So that I don't lose all the oil in the compressor while trying to hook it up, I was thinking of adding 2 at the unit, and then two more down to it through the low pressure hose after connecting the lines in back. Does that sound reasonalbe?

I'll vacuum the system overnight. If it holds, I'll have a shop fill it with N for the pressure test. The cheapest bottle of Nitrogen I can find is $85 after shipping, and a local shop will probably do it for half that. No second chance, though. After a day of watching it, I'll vacuum again overnight, then add the refrigerant.

That's the plan at this point. But, I sure would like to see the actual numbers in the Mercedes 123 AC FSM. Is that available online somewhere? I've read the general rule is a system uses 25% as much oil as refrigerant. That works out to 8.36 ounces. Can anyone confirm the amount?

The manufacturer of the compressor's instructional video says, “Add the other half of the oil charge to the low side of the system. … On TXV systems, add the other half of the oil charge to the evaporator. Do not add oil to the receiver dryer, as this can impede proper refrigerant flow on initial startup as the slug of oil from the dryer works its way through the TXV.”

I'll read some more, but I am not interested in designing a system, or redesigning a system. I just want to replace what there is. But I guess I need to read through someone's struggles with R-12 re-conversion and a debate about what true vacuum is before I earn the right to have air conditioning.

BillGrissom · #14 08-14-2022, 09:45 AM

The oil amount sounds about right as I recall. Best oil for all refrigerants is PAO 68, which I think is what Duracool's Oil Chill is. R-134A is being outlawed, so I would use HC refrigerant (Duracool or Envirosafe). It cools even slightly better than Freon R-12.

You really should re-do your hoses while "in there". The factory suction hose on my 1985 CA 300D began leaking in the middle, as evidenced by green oil on the top of the air cleaner it passes over. Use barrier hose which is much better. I used reduced size -12 for my suction hoses to be smaller. You must cut off the crimp collars on your M-B fittings to re-use. I used new ferrules since have the Master-cool crimper, but Oeticker stepless ear clamps look slick. Can buy all on ebay.

1983/300CD · #15 08-14-2022, 09:45 PM

You're talking about the hose from the evaporator to the compressor, with the break at the low-side valve up front? Not sure if I could tell anything from a visual inspection, but I'll take a look at it. If this compressor bites the dust in the next couple of years (as I almost expect it to), I'll replace it then. I see some of the hoses available online.
I am planning to use the Mityvac to push a couple ounces of oil (I went with ester) down to the half-filled compressor from that break, and the other half of the oil charge (4 ounces) back up that hose to the evaporator. It probably wouldn't hurt to put a couple in the condenser instead of the evaporator, but I'll go with the manufacturer's recommendation.

Then it's just a matter of torque values.
The manufacturer's paperwork says:
Compressor to engine: 40 ft lbs.
Compressor to bracket: 30 ft lbs.(diesel)
Manifold / fitting : 25 ft lbs.

Internet says,
Pipe fittings:
#6 - 11-13 ft lbs.
#8 - 15-18 ft lbs.
#10 - 19-22 ft lbs.
#12 - 24-28 ft lbs.

Lower than I would have expected. Much lower than the torque they used last time putting the system together. The o-rings look like onion rings.