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  #1  
Old 06-04-2003, 01:01 AM
dmorrison's Avatar
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Location: Colleyville, Texas
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Review of my plans for the AC system, comments welcome

I want to post and recieve comments about the rebuild of my AC system.

I have done the typical search but would like comments

I have done just about everything thing to a car but work on the AC system. I was going to get my 609 license but while studing for it I realized that R134 was probably the way I wanted to go (see below). I may still get the license for the SL.

I am working on the 1982 300TD. The conversion to R134 was done about 2 years ago and done incorrectly, I know I did it. I added R134 oil and freon with out flushing or removing of oil. So I now face a contaminated system that will have to be rebuilt. The conversion to R134 was done due to a evaporator leak. It was found by the Dealer with a sniffer. I decided to do the 134 conversion to save money, I thought. The car was an airport car and driven about 2000 miles a year. Now it will become a daily driver and the AC must work well.

This is what I plan.
1. A new R4 compressor.
2. New dryer
3. New evaporator
4. New expansion valve.
5. New parallel flow condensor since I will be converting to R134.
6. All the hoses rebuilt at a local hydraulic shop.
7. New high/ low pressure switch.
8. New O rings with Nylog ( R134).
9. New oil and of course R134a
10. The hydraulic shop will build 2 hoses to allow the new condenser to "fit " to the Mercedes hoses. I want to take this approach so that any future condensor replacement will be a easy job. The alternate is to custom make the main hoses or add a manifold to the condensor so the connections are in the current position. The condensor will be from ACKITS.COM

As I said I want the system to work well since this will be my Wifes and my daily driver.

ANY advise on the removal of the evaporator would be appreciated, I understand its a bear.

R134a vs. R12. I know the sytem is designed for R12. The thought process for converting is so that the car can be a DIY. I understand that the problem with the R12-R134 conversion is a lack of condensor size. Stu Ritter of MBCA fame recommends wiring the AC condensor fan to the compressor clutch. They then find the R134 conversion to be acceptable. I want to solve this problem by going with a larger capacity condensor. So the system will be able to handle the R134. Size for size the parallel flow condensor is 33% more capable then a serpentine unit

The sytem will be dismantled.
All hoses flushed, then rebuilt, then flushed again.
Evaporator replaced, and anything in the dash area that needs replacing will be replaced.
New expansion valve.
New compressor installed with the right amount of oil and once the system is closed rotated to prevent hydraulic lock.
I understand about the oil being hydroscopic and will keep its exposure to the atmoshere to a minimum.
All O rings will have nylog (R134) applied.
The system willl be evacuated to 28" here for Dallas, 603'MSL
Then the R134a will be added by weight.

The last 2 items I may not do depending on the cost of a scale and the vacuum pump. I know the compressor type unit is cheap at Harbor Freight and I have a 6HP compressor that can run the cheapo vacuum pump. I will have to look at the scale cost for this one job.

I may consider an inline filter just for insurance. But with everything new I doubt it will be necessary, as long as I adequately flush the hoses.

My decision to go with R134 Vs. R12 was partially due to the cost of the OEM condensor. Even at Rustys or Fastlane it was $250. The aftermarket unit is $85 at ACKITS.com. The hose assembly to make the aftermarket condenser attach to the Mercedes hoses will be about $60 from the hydraulic shop, they say. The aftermarket Parallel flow condensor has the fittings at the top and bottom of the condensor. The Mercedes unit has it in the middle so some kind of adaptor must be made. The hydraulic shop said that they could weld tubes on the new condensor to place the fittings to the correct place. I did read about having to replace parellel flow condensors with compressor failure due to the small orifice size that is use in the parallel condensor. I would rather make up a hose manifold for the connections which would allow easy condensor R+R.
The current condensor is not leaking but sort of beat up, dirty, bent fins and original. It has also had the R134 oil and the R12 oil in there so the acids may have been eating away at the unit.

I have ordered the "new" CD from Mercedes ( its only $99 for the 123 CD) that will have the AC manual and the Electrical manual that I don't have. When It arrives I will surely have more questions.

Any and all comments and suggestions will be appreciated, Maybe not liked, but appreciated.

Dave

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car
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  #2  
Old 06-04-2003, 07:28 AM
LarryBible
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Dave,

I offer my comments with all due respect. Please don't take offense if I sound sarcastic or anything.

To begin with Stu Ritter does not live in the DFW area where we have an annual heat wave that lasts four months.

You can use a parallel flow condensor and still use R12, it will be all the better.

You are looking at putting some major bucks into this project for obvious and justifiable reasons. Given the overall cost of R12 would represent less than 10% of the overall project cost.

In fact to help you save some money and basically "pay" for the R12 I will loan you my vacuum pump. I am moving toward recovery/recycle machines for my vac pump function and can let my vac pump out of the shop for a week or two when you get to that stage of the project. If you would be charging from a bulk can I would also loan you a "dial a charge" which some folks prefer in place of a scale.

I have converted several 123's with reasonable results, but those results were marginally acceptable because my family and I live 20 miles out of town and do stoplight to stoplight driving VERY rarely. In the DFW area in town driving is almost impossible to avoid.

That said, I have reverse converted one of them.

Other problems with 134 conversion is getting the oil right, and the pressures for that matter. The chance of long term system survival statistically goes down in a converted system. The sightglass becomes close to useless in a converted system, and it usually takes experimentation to get the charge right, even if you carefully meter in what you think is the right amount of 134, you will most likely have to experiment a little by monitoring high side pressure. Once you achieve the right charge, there is no good way to duplicate that volume next time because you don't know exactly what it is. That means experimenting again if you have to charge again later.

An additional comment is to buy a NEW R4. I've been there, done that with rebuilt R4's. If you insist on a rebuilt, do some research and buy one from ackits or somewhere, definitely not a chain store unit.

Best of luck with your project regardless of refrigerant choice and let me know if you want to borrow my pump and dial a charge.

Have a great day,
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  #3  
Old 06-04-2003, 10:36 AM
dmorrison's Avatar
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Location: Colleyville, Texas
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AHHH! the plot thickens.

I will use a NEW R4 Ive heard the stories about rebuilts failing in 1-2 years. That is not the intent of the rebuild. I want to do it once and do it right. So I don't have to worry about it.

I may use the parallel flow condensor and the R12.

I'll start to think in that direction.

Got to go fly a trip and think about my R12 license!!!!!

Dave
__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car
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  #4  
Old 06-04-2003, 11:58 AM
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Join Date: Jun 2000
Location: Plano, TX
Posts: 2,558
Dave -

I think you've got a good plan. Feedback from those who have used a parallel condenser is that R-134 provides reasonable performance. Certainly R-12 is ultimately better, but it may not be truly necessary. At any rate, getting the 609 license is trivially easy - I've had mine since before the internet...

I think the limiting factor in around town performance is the compressor, rather than the refrigerant. At idle, the low side pressure rises to ~45PSI, which means evaporator temp is about 45 degrees. Typically discharge air is 10 degrees above evaporator temp, so think 55 degree air. This is about the upper limit before the air begins feeling clammy rather than cool. I don't know of any way to solve this problem, other than move to the sticks like Larry

One advantage of staying with R-12 is that you don't have to use PAG oil. PAG is nasty stuff - it's a skin and eye irritant, and of course it is very hygroscopic and will certainly introduce water into your system.

One suggestion. The 123 chassis was designed by MB to utilize 80% recirculated air/20% fresh air when in recirculate mode (basically all summer here in Texas). It can be modified to use 100% recirc. I did this back when I owned a 123. I found this mod reduced duct temperatures about 5 degrees on the hottest days. It's quite easy, and well worthwhile. I may have the instructions buried somewhere on my PC.

I've got a vacuum pump and guages, which you're welcome to borrow as well. I bet Larry's are better That said, our offices are across the street from one another (I'm looking at Larry's building as I type this), so it's not like you can save a bunch of driving.

Gotta run to a meeting.

- JimY
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  #5  
Old 06-04-2003, 12:43 PM
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I have a couple comments (I am the guy who converted his '84 300D to a parallel flow condensor and 134a):

1) Is there a particular reason you are going to replace the evaporator? You said it was just replaced a couple years ago. If it isn't leaking then all you need to do is flush it and you'll be fine. Replacing a perfectly good evaporator seems like a waste of time and money.

2) Definitely have the a/c shop install a filter.

3) I did the 100% recirc trick and didn't like it. Here's why. People say there is 80/20 recirc., and I found that not to be true. What happens on my car is the recirculation door opens and closes on some cylce (the system does it automatically). Sometimes the door is closed completely, giving you 100% recycled air, and sometimes it opens, giving you a mixture. I closed it completely for testing and DID NOT notice a significant change in a/c temperatures - maybe only a degree or so. Besides that, I really was unsatisfied with the fact that I had somehow butchered my car and undid something Mercedes had desinged it to do. If you repair the a/c system properly, you WILL have good cooling without jury-rigging the recirculation door. Lastly, its nice to have outside in the car, which you won't have if you alter the system.

4) Jury-rigging the electric fan may be a good idea, but try it first without doing so. If everything is working properly, it will turn on when it is needed, but you can test it later and see if your vent temps are lower. I prefer leaving the car stock when possible.

4) Like everyone says, just go with the r-12. The on-line test is not difficult, and if you are serious about doing the best job you can, you won't waste your time with 134a.

GregS
'84 300D, 174k
'90 300CE, 164k
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  #6  
Old 06-04-2003, 03:28 PM
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It's been a while, but as I recall the 100% recirc modification on the 123 involves the fresh air door, not the recirc door. As designed, the fresh air door is open whenever the climate control is switched on. The recirc door selects either 100% fresh air or 80/20, depending on which position it is in. The modification involves closing the fresh air door whenever the recirc door is in the recirculate position.

I wouldn't worry too much about fresh air in the 20 year old car. A car that age has plenty of air leaks from tired, old, shrunken gaskets and seals.

I measured the performance differnce the change made, so I can state objectively the effect it had. (I keep notes on this stuff.) On a hot Dallas day (105F) it reduced the duct temperature from 58F to 53F. That is enough of a change to be easily noticable; it makes a significant increase in comfort.

Perhaps you don't live in a hot enough climate to require such a change, or perhaps you misunderstood how to perform the modification.

- JimY
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  #7  
Old 06-04-2003, 06:10 PM
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I've "reversed" refrigerant in two of em in the past few weeks. 1982 240D and 1985 300D (got rid of DuraCool in the 300D) and if the ambient conditions are under 90 they will both freeze you out. I am scheduled to do a 1986 Chevy pick up this weekend.
Do what you gotta do and stick with the R12.
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  #8  
Old 06-04-2003, 09:19 PM
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Whoa there big fellas!!!!

I knew I would get a lot of info. Let me let you know what I have considered.

Larry
Thanks for the info and ability to borrow the vacuum pump and the "dial a charge". I think I'm going to go with the R-12. (good boy they all say, What a man, A true R12 man *G*)
I wil get the 609 license and then be ready for the 300TD and the 560SL.
But I am still thinking about the parallel flow (PF) condensor for better cooling and to save $200.
My understanding of the AC system is that the R134 freon can not be cooled suficiently in the serpintine condensor due to the design heat exchanging ability of the unit. It was not built to exchange the calories that the R134 needs. By using R12 in the PF condensor I will ensure that the R12 is completely sublimated from gas to liquid, even though it may be 110F outside. The stop and go traffic in the metroplex agrivates this by reducing the airflow over the condensor. By using the PF condensor I will help the system provide adequate liquid freon to the expansion valve therefore allowing the evaporator to have the necessary cooled freon liquid to expand. By using a larger capacity (a PF condensor) I will make the system work better.
Do you see any system problems using the PF condensor with the current 123 setup which I will be renewing?

Jcyuhn
I will look into the ability to close the fresh air vent completely. Can this be done after the dash is reinstalled or does it have to be done while I have the interiors of the car out?

GregS
The evaporator was NOT replace by the dealer. They found a leak that was small. I had them remove the R12 and I put the R134 and 134 oil in the system. Then every couple of months I was going to top off the system. So the evaporator is still leaking and will need to be replaced.
Would you still recommend a filter when everthing in the system wiill be brand new except the metal sections of the hoses, which will be flushed completely?

moraine
I will check with Tim at ackits.com. but now I have been "saved" and will go with R12.
I would still like to go with the PF condensor. Unless you guys can convince me to spend $200 more for the OEM replacement.

To all

1. A NEW compressor
2. R12 R12 R12. R134 is the devils work. Say amen. *G*
3. I will rebuilt the hoses, they are 23 years old.
4. Condensor is also 23 years old and will be replaced, the acids have been sitting in them
5. Flush Flush Flush and Flush again. Ok another amen.
6. I will look into the fresh air door modification. again If anyone has the specifics please let me know.

Well I hope I have not offended anyone.

I just bought R134 guages form Harbor Freight, I'll have to return them. I will work on the 609 license and start taking this system apart. order the necessary items ( talk to ackits and Rusty) and get moving on the project. any other words of wisdom will be great.

Now who was going to help me with the removal of the dash and center consol?????

Once I get the service CD I'll have questions I'm sure.

Dave


Ahh questions all ready

1. Tightening the fittings. Double wrenches, but to what torque? Do you actually torque them with a torque wrench or guestamate them?

2. Methods of keeping the moisture out of the system? I'm sure you use caps on all the components. Hoses, dryer (should come with caps?) compressor? evaporator etc. What methods do you seal the various parts with.

3. Applying nylog, How much and where? Orings? threads of connectors? etc.

4. Does the Service CD have an exploded view of the evaporator section. If so could someone Email it to me dwmorrison@attbi.com

thanks guys
__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

Last edited by dmorrison; 06-05-2003 at 12:20 AM.
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  #9  
Old 06-04-2003, 10:56 PM
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Location: Plano, TX
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Dave -

One more thought. Not to pile yet more work upon you, but consider replacing/rebuilding the vacuum elements while you have the dash apart. At the bare minimum replace the element for the center vents - it's inaccessable without removing the dash, and is usually the first to go. My hazy recollection is the other elements on a 123 can all be replaced without pulling the dash. (Someone please correct if I'm wrong.)

Modifying the system to use 100% recirculated air is quite simple, and does not require dashboard removal or any surgery. It's about 10 minutes work and requires about a dollar worth of parts. It is completely reversable should you not like the results. Here's a link to an article I wrote (in 1999!) on how to implement it. This is the archives of the original mercedes mailing list, which predates this bulletin board by about 7 years...

http://db.mercedes.cx/mb/199904/15/0010.html

The searchable archives of the mercedes mailing list are available via http://www.mercedesmailinglist.com

Good luck and enjoy,

- JimY

ps - I vote for the parallel condenser too. Why spend extra for the MB unit?
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  #10  
Old 06-04-2003, 11:58 PM
dmorrison's Avatar
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Location: Colleyville, Texas
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jcyuhn
I do believe in doing it right the first time. My Father taught me this because he was so cheap that he once tried to epoxy a fuel pump diaphram to see if it would work. This drove me nuts and I learned to do it right the first time.
I will look at everything as I remove the dash and take care of it as I go. The elements will be replace because I'm there. I sort of did this with the suspension rebuild. EVERYTHING in the suspension was replaced. It lasted 23 years so the next 23 years I don't have to worry about my suspension.
My sons 65 Mustang turned into a 2.5 year restoration due to the inevitable "while I'm at it itis" that comes with car repair.
The 300TD is turning into the daily driver. Were going from the 99 E300 as a daily driver to the 82 300TD ( I'm a pilot for American Airlines, Were still not out of the woods when it come to filling for chapter 11. Its looking better, but were not celebrating yet. so the 300TD will be the car of choice for the next couple of months/years) So the 300TD needs to be in great shape. Its hard to go form 99 E300 luxury to the 82 300TD and " not notice". A suspension rebuild and a cold AC in Texas will make the transition easier. I've owned this car since 1990 and have always liked it. So this just presents the opportunity to "restore" it to the level I want it.

I have saved the sites that you have shown and will look at them tomorrow.

KEEP THE INFO COMMING GUYS

Thanks

Dave
__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car
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  #11  
Old 06-05-2003, 01:19 AM
1991300SEL's Avatar
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And here's similar info as presented above, only for the 126 car. At this same site there's also discussion on parallel flow condensors:

http://business.baylor.edu/Richard_Easley//autofaqs/recirc.htm
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  #12  
Old 06-05-2003, 01:22 AM
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Location: San Francisco, CA
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Dave If it is any encouragment, a 300TD that is right (suspension etc all refreshed) is a great driver. Mercedes sold a ton of them and theres got to be a good reason.

I recently rode in a 1978 240D with 78k miles. I was very curious what it was going to be like. The 123 model cars are remarkable. I quickly enjoyed riding in the 78 and remembered why I bought several of them.

Keep us posted,

Haasman
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  #13  
Old 06-05-2003, 06:32 AM
LarryBible
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Dave,

The nylog only needs to go on rubber parts, you need not use it on threads and such.

You don't need to torque the connections, just snug them up tight with a back up wrench.

The parallel flow condensor for LESS money is a no brainer. Since you have to replace the condensor anyway, and your building new hoses anyway, you will not only save money but also will have a more efficient system. Although there are other variables, the "capacity" of any air conditioning system is almost always determined by the condensor heat exchanging capability.

I have to pass on your offer to let me share in the fun of tearing apart the dash. I think that would just be more fun than I could stand.

Good luck,
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  #14  
Old 06-05-2003, 12:23 PM
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Location: Land O Lakes, FL
Posts: 3,086
Dave, it looks like you're seeing the light. One thing I want to mention that has not been hashed over is the vacuum pump. I'd suggest you borrow Larry's pump rather than buy the compressor operated one. We had a debate about this recently and he won. I have the Robinaire pump, which is supposedly better then the Harbor Freight unit. When the subject was debated, I went out to the garage and tested the pump. It managed 27" with nothing connected but the gauge set and I'm virtually at sea level in Florida. The compressor ran continuously, so leaving it on all day would not be a nice thing to do to it.

If you need to hear it again, the parallel flow condenser with R12 sounds like a great thing.

The R12 license online is ridiculously easy - had mine in under 1/2 hour.
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Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
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  #15  
Old 06-05-2003, 10:25 PM
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Posts: 459
A couple more comments:

-I have the PF in my car and I can't think of any drawback besides the nuisance of fabricating custom hoses. Go for it.

-If eveything is going to be new, what is there left to flush? You already have a huge job ahead of you, so don't make it worse than it already will be. Still go for the filter though.

-I stand by my comments on the recirc. door "trick." No disrespect jchyun, and maybe my car is special, but it didn't work. I used your link a year ago to do this mod., and on my car the system would cycle a couple times and then the recirc. door would no longer open and close until I turned the car off. Something in the switch system would not allow my car's doors to open and close as you claimed they would. I drove around for a couple days with the glovebox out just so I could easily observe what was going on and to be sure of my conclusion. If it were my car, I would maybe rig up the electric fan to turn on when the compressor is running, but I wouldn't bother with this particular mod.

-When I did this job the advice given by the guys that sponsor ackits.com was to use Nylog on, and I quote, "everything." O-rings, threads, service valves, service valve caps, etc. It can't hurt.

-Just snug up the fittings with the wrenches. These are all light aluminum fittings, and the o-ring is actually doing the sealing work, so don't go too hard on the fittings.

GregS
'84 300D, 174k
'90 300CE, 164k

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