Mercedes-Benz Forum banner
1 - 20 of 20 Posts

·
Registered
1991 350SD
Joined
·
27 Posts
Discussion Starter · #1 ·
Hi Everyone, I searched the forum, there is quite a bit of useful info on the topic but I need some experience based advise here.

1991 350SD

I had my mechanic refill the AC last summer with R12 and it lasted most of the summer. This year car was in for service for a lot of things and I asked him to put dye in so we can eventually find the leak, he said dye tends to destroy the system and he also forgot to refill the refrigerant as well (also didn't charge me so fine).

I want to accomplish a few things, refill the refrigerant myself. Is there a kit someone could recommend that they used with good result. I'm not sure if I should just fill the system up or do the complete process, evacuating whats there and refilling it. So need best advise there.

Secondly I do want to find the leak. Has anyone had any success using sniffers. If not what was a good method that you used, if you used dye and your system remained in tact which one did you use?

Thanks in advance,
Mike
 

·
Registered
1986 420SEL x2
Joined
·
60 Posts
I have yet to find a reliable sniffer that warrants the cost the number of time used (once). There are some posts on the negative effects of the dye on the system which I discount as the dye is innert. My choice is to use one of the refrigerants R12 compatible (MSDS shows it is mostly 68476-85-7 LPG (propane) with a dye. At less than a fiver you can load the gas and look for leaks.
 

·
Registered
1991 350SD
Joined
·
27 Posts
Discussion Starter · #4 ·
I have yet to find a reliable sniffer that warrants the cost the number of time used (once). There are some posts on the negative effects of the dye on the system which I discount as the dye is innert. My choice is to use one of the refrigerants R12 compatible (MSDS shows it is mostly 68476-85-7 LPG (propane) with a dye. At less than a fiver you can load the gas and look for leaks.
Thanks is there a product you can recommend?
 

·
Registered
1986 420SEL x2
Joined
·
60 Posts
Red-tek, Ultra cool there are a number on the market. Cheaper is better as you are only looking for leaks. One can should do the job. I have a UV flashlight to help when I check a night. My guess is the shaft seal on the clutch side of the compressor maybe leaking (common).
 

·
Registered
Too many to list
Joined
·
11,426 Posts
There have been many past threads on this topic, and the best solution I have found is to use in Envirosafe

it works as well as R12 and does not leak out as easily due to the larger molecule structure. The refill kit cost only $28 and it does include dye

I have use this kit on at least six cars with leaky systems, and it usually lasts all summer, and in one case it has lasted for several years.
 

·
Registered
1991 350SD
Joined
·
27 Posts
Discussion Starter · #7 ·
There have been many past threads on this topic, and the best solution I have found is to use in Envirosafe

it works as well as R12 and does not leak out as easily due to the larger molecule structure. The refill kit cost only $28 and it does include dye

I have use this kit on at least six cars with leaky systems, and it usually lasts all summer, and in one case it has lasted for several years.
Thanks, think I'm headed for the envirosafe with dye just not the stop leak.

Does anyone know what the pressure should be when it's full?

Thanks in advance
 

·
Super Moderator
1986/1990 W126
Joined
·
19,901 Posts
There have been many past threads on this topic, and the best solution I have found is to use in Envirosafe

it works as well as R12 and does not leak out as easily due to the larger molecule structure. The refill kit cost only $28 and it does include dye

I have use this kit on at least six cars with leaky systems, and it usually lasts all summer, and in one case it has lasted for several years.
Someone on another section said this product label indicates its a liquid petroleum gas based thing. Found that interesting, made me think of our members who use Propane in their systems.
 

·
Registered
1986 420SEL x2
Joined
·
60 Posts
I would avoid anything with a leak prevention as you are trying to find the leak. There could be many reasons for a leak and some are rather simple. LPG, propane or R-290 is the dominate gas in the recharge with each manufacturer using their own combination. To accurately check the pressure you need a gauge for r290. If you do not have one you need to calculate how many ounces can be applied. In your case https://www.4s.com/media/7228/capacityguide_4season_2020.pdf claims 45oz of r12. Doing the math based on a gas https://fire.lacounty.gov/wp-content/uploads/2019/08/Gas_Conversion_Chart.pdf an empty system should take 28 ounces of propane to fill. If you think the leaks have been addressed try one can as they are usually 14oz. Put a thermometer in the vent to monitor the temp as it should be less than 50F (10C). The bubble in the window is not a reliable indicator with this gas. If the temp is not down add the second can knowing you are at capacity.

I acknowledge there is much debate on the use of propane as a refrigerant gas.
 

·
Registered
91 420SEL, 72 350SL, 99 S600, 05 Ford F-350, 09 C300, 10 Boxster 987, 12 GL450 , 87 560SEL ,05 SL60
Joined
·
524 Posts
Hi Everyone, I searched the forum, there is quite a bit of useful info on the topic but I need some experience based advise here.

1991 350SD

I had my mechanic refill the AC last summer with R12 and it lasted most of the summer. This year car was in for service for a lot of things and I asked him to put dye in so we can eventually find the leak, he said dye tends to destroy the system and he also forgot to refill the refrigerant as well (also didn't charge me so fine).

I want to accomplish a few things, refill the refrigerant myself. Is there a kit someone could recommend that they used with good result. I'm not sure if I should just fill the system up or do the complete process, evacuating whats there and refilling it. So need best advise there.

Secondly I do want to find the leak. Has anyone had any success using sniffers. If not what was a good method that you used, if you used dye and your system remained in tact which one did you use?

Does anyone know what the pressure should be when it's full?
Thanks in advance,
Mike
Get a new mechanic (understand why he does not want to fool around with an old system)! The part about dye damaging the system is pure BS - has been successfully used for years with no harmful effects. You will need a good UV light made specifically for detecting the dye to find the leak (no cheap lights) and it may well be in an inaccessible place like under the dash. Sniffers sometimes work with a large leak, but the dye system always works. There is no R12 legally available for sale in this country - the stuff they sell is a substitute made mostly of propane with some other hydrocarbons and CFls. It works better than R134a (which requiresa full flush and change of oil). but still no wheres near as good as the old R12. If your system still does not cool well after finding the leak and filling with the R12 substitute, the only alternative is to replace the system with an R134a system which will requre a new condensor coil and expansion valve and possibly a new compressor and possibly some changes under the dash.. R 134a operates at nearly three time the pressure of the old R12 systems and is not as an efficient refrigerant medium. Listen to @Doug320.
The manufacture of the R12 substitute should supply you with a refrigerant chart appropriate to the particular combination of gasses used that shows the high and low side pressures appropriate to the ambient temperature - there is no "one pressure fits all" for refigerants.
 

·
Registered
1985 MB 500sel (Euro)
Joined
·
1,173 Posts
I had good luck switching to 134a, but it was an unusual situation. Others have also been successful (@MBL87560SEC) with 134a I think. But, Gumpy's advise is right on if you don't want to try Enviro.
 

·
Registered
1986 420SEL x2
Joined
·
60 Posts
If you do convert all of the O-rings must be changed. This is why people just replace replace the part and get a new set of rings. In the case of my 1986 the expansion valve is, without question, the hardest repair on the car.
 

·
Registered
1986 420SEL x2
Joined
·
60 Posts
Also in the conversion you will have to complete a thorough AC system flush (not hard but it takes time and the you have to remove the expansion valve).
I would try the substitute and then if all fails convert. I run the substitute and find it works well but then I don't need it most of the year.
 

·
Moderator
1987 & 1991 C126
Joined
·
6,253 Posts
I had good luck switching to 134a, but it was an unusual situation. Others have also been successful (@MBL87560SEC) with 134a I think. But, Gumpy's advise is right on if you don't want to try Enviro.
My 1987 SEC came with R-12, and remains so today, some 19 years later.

The '91 500 Euro had R134 from new, has had a compressor & drier replacement roughly 4 years ago...

The ACC is very nice in both.
 

·
Registered
Smoke Silver '87 560SEC, Black Pearl '87 560SEL
Joined
·
4,641 Posts
Seems to be a lot of misinformation here. R134 pressures are about the same as R12, not triple the pressures. At 80F, the R134 charts say 175-210 psi. Using R12/Replacement R12/Propane, I set the high pressure to 200PSI and get GREAT cooling.
The o-rings are the same for R12 and R134 so they do not need to be changed out. If the o-rings are original, 30 something years old, then change them for reliability sake. Get a kit of green Viton o-rings at the local auto parts store and use them instead of the black o-rings. A new o-ring does not need to be exactly the same as the original one. I replaced 13 o-rings in my '87 560SEC with the greenies, with o-rings kinda close, and it's holding great several years later. I get 15F-20F air out of the center vent with 100F Las Vegas temperatures.
BUT...R12 requires an Ester based compressor oil while R134/R134a requires a PAG oil. Or just buy a synthetic compressor oil that works with both.
 
  • Like
Reactions: John350

·
Registered
300 CE 24V Sportline
Joined
·
1,740 Posts
My a/c was brought back to life in 2107 by an MB independent on the south coast of England. The 1991 300CE had an R12 system, obviously, but it now has 134. And it works, 5 years later.

I run it every now and again to circulate the lubricant and, whilst it's not frigid, it is entirely adequate and was a great relief on a 2 hour journey with ambient close to 40C.

We have an evaporator and heater matrix in stock for that dreadful time when the dash needs to come out after the warm blue feet experience that may son had. He did the dash out job so he'll be enlisted when mine gives way!

RayH
 

·
Outstanding Contributor
'17 GLS450, '14 GLK250 "Grandpa's Roadster" Project Car, 350SDL (Sold)
Joined
·
5,291 Posts
I set the high pressure to 200PSI and get GREAT cooling....I get 15F-20F air out of the center vent with 100F Las Vegas temperatures.
That's amazing! But, don't try it in Florida! With any humidity, the evaporator will freeze up and you'll get no airflow. Best to adjust the pressure so the low side is a couple of degrees above freezing.
 
1 - 20 of 20 Posts
Top