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1999 500SL, 1988 SEC
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Discussion Starter #1
I have decided to refurbish my ac this fall before winter sets in. I will be changing it to R134 instead of R12.So far I have new transverse condenser, new expansion valve, new drier and two switches. So my questions are
1) After I open the system up I know I need to flush it. Is it is simple as taking the hoses off the compressor and flushing it with acetone? I assume I should do that before I put the new expansion valve on. How do you flush the compressor.
2) After flushing it out how long can I keep the new unfilled system open? I would just cap the lines. It will take me some time to get new hoses made and do the other work.
3) Where are all the O rings you have to replace. Just on the compressor, is there a kit?
My real big debate is whether to remove the dash. I have all new pods so its not neded to do that but by removing it I can clean the heater core and the evaporator. I can also look at the blend doors. Downside is its one hell of a lot of work. We will see. Another muffin for the Moose I guess
 

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W126 1990 500SE (ASR) & W126 1991 300SE
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233 Posts
I'm not an expert on AC, but I did recently have my condenser, compressor, dryer and expansion valve changed. I actually worked alongside the technician, in order to gain some knowledge and experience in these areas.

I'm not aware that the system needs to be flushed, and acetone might have a detrimental effect on any plastic or rubber parts, including the seals. The first step should be to check for any leaks in the system by evacuating any gas, and seeing if it holds a vacuum. I have only heard of flushing, in a case where some contaminant has entered the system (black sludge from a damaged dryer/compressor for example). Hopefully others can chime in on this.

The conversion from R12 to R134a doesn't requiring changing any of the parts you've mentioned, so are you changing them due to a leak?

It is possible to replace the expansion valve without removing the dash. To do this job properly you'll need large open ended crowfoot wrenches...I forget exactly the sizes you'll need, but they range from about 19mm-24mm. The valve itself has 4 connection points, two on the high pressure side, and two on the low pressure. They all have different sized fittings, so that a mistake cannot be made with installation, and you will need new O-rings for all 4 connection points. The trick with replacing this part is to make sure you use a large wrench to hold the valve itself, while you break open each of the 4 connections. They are, of course, all hard line connections, and it's important not to allow the connections or the valve to twist from its position, otherwise you will have great difficulty getting those hard lines to seat correctly when you fit the new part.

I don't know if there is a repair kit for the compressor. Of all the parts I would replace, it would be the compressor. This is the most common AC component to leak on our cars, and I think the original MB compressor (designed for R12) is the part most vulnerable in a R134a setup.
 

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One Smoke Silver '87 570SEC, one Black Pearl '87 560SEL
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I'm too lazy to type all this out. Give me a call and I'll help. 702-four nine four - eight zero five six.
 

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1989 300SE 232k miles
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1,656 Posts
If you’re taking the system apart, flushing it is easy if you have an air compressor and the right gun/tool. You simply attach the gun at one end of the hose/line, blow cleaner, then blow air (and have something to catch the cleaner at the other end). I used the four seasons brand cleaner. One bottle should be enough, it’s pretty inexpensive, and will evaporate.

So long as you use a cleaner that evaporates, and you vacuum the system properly, you can leave the system open as long as you’d like. Vacuuming the system after you put the new parts together should remove any moisture, and that’s the concern.

The o-rings will be self-evident as you take the system apart. They’ll be at every locking joint. There is a special gasket for the compressor, but otherwise the rest are generic. They sell kits with all the o-rings plus the one for the compressor. Or you can buy a generic AC o-ring kit.

I bought a generic kit with like 200+ o-rings. Now I have more than enough for everything else, but none for the compressor.

Once the system is empty, working on it is not difficult. Martin_UK’s suggestions are great. The hard part is going to be the interior stuff. And making sure you have the right tools. ...I had to buy huge wrenches for the nuts in the engine compartment. I simply did not own a 1 1/4 inch wrench.
 

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1989 300SE 232k miles
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1,656 Posts
Ya know, flushing is to get rid of oil and crud from the old system. If you’re replacing everything and having new hoses made, I don’t think you need to flush the system.
 

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1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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4,876 Posts
Hi there John,

As you will be changing from mineral oil to PAG oil, I agree you will want to flush.
Knowing you through our conversations, I would remove the dash, and remove the entire ACC box for the refit.

Unless you want to try to clean the inevitable crud littering the evaporator leading face from up & underneath, R&R the unit would be the way to go.
Another removal 'benefit' would be one could refresh all the airflow door seals & any failed linkages along the way.

I think you mentioned you had a line on another Gen2 ACC unit to overhaul, then swap into your SEC. Obviously, that would be ideal to these eyes and all your 'new' vacuum actuator pods
could be swapped over easily before re-installation, as they would be right out in the open.

Isthenew & Martin give great advice for cleaner/flush, o-rings, and expansion valve machinations. He's right, it can be done in situ. I did this in 2016. I used a medium 'needle-nosed' Vise-Grip pliers as a counter hold against the 4 A/C line connectors up in there..

At the risk of repeating myself, do get a new A/C hose grommet for the firewall just by the brake booster.
As was mine, I am sure the one on yours is past questionable by now. 126 997 05 81.

M.

IMG_0460 2.jpg
 

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1999 500SL, 1988 SEC
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1,415 Posts
Discussion Starter #7
Thanks to all and mramay, I will call. I think the compressor also has to be flushed to remove the old oil. We will see on the dash. Malcolm your correct it is the ultimate but also gain vs pain. I use the air so little that while it would be great to fix all the seals on a heater box, its also a lot of work. At any rate I started this thread and as I do the project I will update it for others. There are lots of threads on changing to R134 but not many on installing the new condenser and such. Good luck to all
 

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1985 MB 500sel (Euro)
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Lots of comments on past threads about benefits of switching from hard to find R12 to some other. Just my experience, I went to R134 and found it did not cool the car enough. Ok perhaps for the UK (before climate change?) but not Florida. So I went back to R12. Yes, its (much more) expensive but as long as the system works (fingers crossed) I'm much happier with it and more importantly, so is she who must be obeyed.
 

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1999 500SL, 1988 SEC
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Discussion Starter #9
Yes, that is why I went to a parallel condenser if I am going to R134. By doing that the change should be ok. . I figured if I was changing the expansion valve, I might as well do the dryer, get new hoses and put the correct condenser in. The R12 was struggling. Its one of my winter projects
 

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1985 MB 500sel (Euro)
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I think I understand what you are doing and I look forward to the step-by-step description for if and when I need to go to R134 also. And also, if it works for Michigan summers. My last fill-up with R12 is about five years ago. So far so good, but fingers crossed and be prepared.
 

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1985 MB 500sel (Euro)
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I think I understand what you are doing and I look forward to the step-by-step description for if and when I need to go to R134 also. And also, if it works for Michigan summers. My last fill-up with R12 is about five years ago. So far so good, but fingers crossed and be prepared.

Edit: sorry for the duplicate. foiled by the computer again.
 

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One Smoke Silver '87 570SEC, one Black Pearl '87 560SEL
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Couple of points. Flush everything as mentioned but put in a synthetic compressor oil. The synthetics don't care if you are running R134, R12, or R290. Save you some effort later when you realize that R134 is quite inefficient in cooling these cars and you want to go to another refrigerant. I used TSI Supercool A/C Comp Ester Lube, which is compatible with both PAG and Mineral Oil systems. Also, it's made in USA. No affiliation, YMMV.
Anyone that wants to try R290 (propane!), give me a call. I've been using it for over five years and get 15-20 degree air from the center vent with 105+F outside temps.
 
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1986/1990 W126
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Mramay should know. Your temps are amazing. My air con bloke won't do propane. But then we don't necessarily need it.
 

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W126 1990 500SE (ASR) & W126 1991 300SE
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Lots of comments on past threads about benefits of switching from hard to find R12 to some other. Just my experience, I went to R134 and found it did not cool the car enough. Ok perhaps for the UK (before climate change?) but not Florida. So I went back to R12. Yes, its (much more) expensive but as long as the system works (fingers crossed) I'm much happier with it and more importantly, so is she who must be obeyed.
But don't you have an issue trying to find the R12 gas? Here in the UK, it's impossible to find anyone who has it.

I've heard that R12 is much better, but I have two cars, both with R134a. One is 'ok' for AC, the other is absolutely amazing! I should get a thermometer so I can check the temperatures, because it's almost 'too' cold, if such a thing is possible!
 

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Mramay should know. Your temps are amazing. My air con bloke won't do propane. But then we don't necessarily.
Over here in The Colonies, propane is "not approved". It's not illegal, but it hasn't been approved for use in cars like Japan and, I believe, middle east. A licensed shop cannot put it in, but I can. My guess is that it isn't approved because it costs under two dollars ($2.00) to fill the system and there isn't much profit in that. Follow the money....
R290, the more refined propane, is used in buildings and RVs and is similar in cost to R12. Hardware store propane works just fine. Several years ago I had a shop recover the R134 in the system, flush it, put in an Ester oil, and give the car back to me under vacuum. I put in the propane. Took the 560SEL to a Mercedes shop here in Las Vegas a few weeks ago because I'm too lazy to replace the #$%^& expansion valve and he didn't have any equipment to recharge R12! Could do R134 but not R12. He replaced the receiver/dryer too and gave me the car back assembled but not under vacuum. I pulled the vacuum and filled the system. It's getting to be that I know as much as the shops on a 126 AC system only because their mechanics don't work on them much. Guess that means I'm getting old!! :)
 

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1984 500SEL
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If you want to practice on one before you jump into your project, I volunteer mine. :)

Good luck! As this project is on my to do list as well, I look forward to your updates.

Jason
 

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1985 MB 500sel (Euro)
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But don't you have an issue trying to find the R12 gas? Here in the UK, it's impossible to find anyone who has it.

I've heard that R12 is much better, but I have two cars, both with R134a. One is 'ok' for AC, the other is absolutely amazing! I should get a thermometer so I can check the temperatures, because it's almost 'too' cold, if such a thing is possible!
R12 is available but you have to ask around and it is expensive. If R134a works for you, I would say the best of British luck to you and don't worry.
 

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1989 300SE 232k miles
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I was at the U-pull-it yard today grabbing a couple parts off an ‘87 diesel. I’ve taken things from it before and decided this time I’d pull enough to look at the expansion valve and the vacuum pod next to it.

I got there and those were both exposed. I looked at that expansion valve. I’m gonna say, after looking at that, getting the expansion valve out looks like a super-pita. Does removing the line on the left side give you access to the line on the right? Cuz it’s damned near inaccessible.
 

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1999 500SL, 1988 SEC
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Discussion Starter #19
Well today I started the project and I know it will take me many months but I will come back to this thread and update things. Here goes.
1) First thing I did a while ago was to start amassing parts. I purchased a new parallel flow condenser from Klima works, a dryer, high pressure switch.
, and. A low pressure switch. The condenser came witha couple of hoses so I will have to figure hoses out later.

2) Evacuate the old freon using a recovery tank.
3) Remove the drivers side snorkle and the piece on the front radiator support. There are two bolts on the support and a pushpin on the bumper side. You remove this to get easier access to the lod dryer.
4) Break the two lines off from the old dryer and unplug the pressure switches. Unbolt the dryer. It is held to the inner fender by two #8 sheet metal screws. Remove the dryer and put on the bench.
5) Jack up the drivers side, put a jackstand under it and at the back of the compressor where the lines go into it you will see an allen tyoe bolt holding both lines to the back of the compressor. Remove it. You will also see a allen type bolt holding an accumulator can to the block. Remove that but once you have the can off put the bolt back for now since it is an oil passage.
6) Disconnect both ends of tha ac lines goingto the fuels cooler. I used two cresent wrenches.
7) U fortunatelyto remove the condenser you have to remove the radiator.......... So drainthe radiator from underneath. Unhook all the upper and lower radiator hoses.
6) Disconnect the two transmission oil cooler lines. Have a pan underneath since you will loose some.
9) Unhook the radiator shroud and move it back.
10) You should be able to remove the radiator now by simply lifting it out.
A comment here. That line going from the fuel cooler to the expansion valve is going to be a bugger. I suspect I will have to remove the false firewall.

Thats it for tonight. More tomorrow I think
 

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560SEL 560SEC 300SEL E320 Cab. MB Metris Van / 300TD 300TE 300SDL, 300D, Unimog 406 (Gone)
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But don't you have an issue trying to find the R12 gas? Here in the UK, it's impossible to find anyone who has it.

I've heard that R12 is much better, but I have two cars, both with R134a. One is 'ok' for AC, the other is absolutely amazing! I should get a thermometer so I can check the temperatures, because it's almost 'too' cold, if such a thing is possible!
I think R12 is hard to find in the EU. But here it is no problem and with several cars that were not converted I don't think I spent $200 on R12 and I have 5 cans sitting on the shelf. I can't compare, but my a/c guy says R12 works better.
 
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