tough questions for A/C specialists
 

My 82 380sl (euro) was converted to R134 last year at that time I replaced the compressor and dryer. The A/C was moderately cool but never strong (my 400E A/C is very strong in comparison). MB service said this was all the euro models A/C put out and the US spec cars had better A/C. Now I have a slow leak in the A/C but the tech finds no leak with dye or the "sniffer". Suggestions for the next step? Can I replace the condenser and evaporator with more efficient (later model/design/aftermarket/or U.S. spec) components. Monovalve was rebuilt and is working correctly. As a good d.i.y. mechanic is changeout of evaporator and dash dissasembly within my means? Any special tools needed? Any gray market SL owners out there with strong A/C? All experience and suggestions are appreciated.

Thanks
Jim (JRJ)

First what makes you think to replace the evaporator? Just cause they cant find a leak doesn't mean it is an evaporator, tis isnt something you want to replace just to replace it. When I have one that has a very small leak I charge the system and leave it in an enclosed area overnite so I can detect the leak. Also if it is a euro model what kind of compressor was installed on it, some are a sanden ( hope I spelled right) and some are regular a-6 compressors ( big long one down below on drivers side. If it is an a-6 these dont work well with 134 conversions. There is no aftermarket drier or evaporator to make it cool better. My suggestion would be to find the leak ,fix it.
Then depending on what compressor it uses , if it is sanden it should cool ok with 134, if it is a-6 go back with r-12 , I know its expensive but if you want it to cool correctly thats what you do. Good luck:D

I appreciate your advice. The MB mechanic implied that the leak probably was in the evaporator core. Obviously more testing needs to be done prior to any agressive dissasembly work. The compressor on the car is a remanufactured from Four Seasons part#57033. The compressor is approximately 9 inches in length including the clutch pulley. Is the the A-4?

JRJ

Ok thats probably the sanden unit , have him look at the pressures at idle if they fluctuate take it off and get a good one. I tried for seasons compressors along time ago and they dont last. You can get a new unit for pretty cheap ( bmw conversion uses this compressor on older cars ) Make sure he locates the leak, and fixes it . Then make sure you get your pressures right at idle ( DO NOT go by bubbles in sight glass on 134. you have to put in 15% less 134 than the car originally had r-12. I go by pressure and put a thermometer in the dash and adjust that way sometimes. Good luck.:D

Did they change the AC hoses when retrofiting to R-134? R-134 gas molecules are smaller than R-12 and can bleed through the hoses. It was first thought that barrier hoses were needed to prevent R-134 from bleeding through the R-12 hoses. It was found though that the R-134 oil would soak into the R-12 hose and establish a barrier to prevent R-134 from bleeding through the hose. However, the old R-12 hose has to be in good condition or the R-134 oil will not establish a barrier to prevent the R-134 from bleeding through the hose. On my '77 I had to replace both of my hoses about 5 years ago because they leaked along the entire length. You can have the hoses rebuilt by many AC supply houses with R-134 barrier hose and at a very reasonable cost (I'm talking about home and business AC supply houses and replacing the hose portion using your old metal ends).

I second euro 287's good advice to let the car sit overnight to let escaping R-134 collect enough to be detected. I'll add to not stir-up the atmosphere before testing to find the escaping gas (like opening large doors to let the breeze in, turning on fans, etc.). Also good advice about charging the system.

Not cooling well can also be caused by too much oil. R-134 does not work as well if the oil content is too high (too much oil can also kill your compressor). Mixing the two different kinds of R-134 oil (POE and PAG) can also cause cooling problems. Also, R-134 oils absorb moisture more readily than R-12 oil and moisture in the system can also cause cooling problems requiring a good deep vacuum (27+ inches of mercury) drawn on the sytem to remove it.

Good Luck!
Tom

As to finding the leak, I use the flourescent dye method eventually. I say eventually because even if we detect with an electronic detector we want the dye stain to show us how it leaked.

As to whether you can improve the A/C. Is the A/C a factory unit or was it afterinstalled? The 107 bodies worse problem was volume of air delivered. Most hang-on units were added externally to the case, which caused them to be small and not situated to take advantage in the poor airflow condition. If this is the case I would consider a DIY project installing a used factory evap case (w/new evaporator) of whichever system the car has. This would cost a fortune if done professionally, mainly because it is one of the worse evap jobs going. Lots of pitfalls.

I would redo it in R12 no matter what system it was. After doing hundreds of conversions, I find them often less efficient. if its a marginal system in R12 then it is likely to be poor in 134.

I appreciate all your advice and suggestions. The A/C is in dash and I presume factory installed, not a below dash add-on system. The A/C lines were not changed with the R134 conversion. Your technique on overnight observation prior to using the sniffer I will pass on.

Obviously job one is to find the leak. Getting the pressures correct are reasonable first steps. Rechecking the compressor, going back to R-12, and changing the A/C lines sound like a good plan.

Thanks to all
Jim

There sure would never be anywhere to hang a unit under the dash on an SL.

Just because the face of the console looks like A/C controls doesn't mean it was factory installed. it is an important question to ask your tech. If the car has Climate control it undoubtably was a factory install. If it was manual A/C then the fact and most all aftermarket used the same console controls. The problem has to do with how they installed the evaporator.

I'm sorry I misunderstood the question. I have a friend with a 69 280SL with an add-on under dash A/C. I have dual temperature wheel controls, and compressor and recirculate switches and a sensor on top of the dash. I don't know if this is enough information to tell if this is a factory or add-on install. I will inquire with my mechanic.

Thanks again
Jim

This is my car's A/C controls. I don't know if the photo helps.
[IMG]d:/sl_dash.jpg[/IMG]

Thanks to all
Jim

If you have a Sanden compressor, keed in mind that they are actually pretty good compressors. But, the best thing about having a Sanden unit is that a Diesel Kiki compressor should swap right on, and the Kiki's are said to be one of the best compressors out there. Just search the internet and do some price comparisons. You can get rebuilt units for less than $200. Give www.ackits.com a try.

Greg
'84 300D

P.S., yes, there is an improvement you can make to your system, and its called a parallel flow condensor. This is the type used on new cars that have 134a installed at the factory. Again, check out the prices at www.ackits.com

Greg

I don't see the picture but it wouldn't matter. You describe the standard manual A/C (as opposed to automatic A/C - Climate Control) controls on the console. These ARE the controls used by most aftermarket installs (done in Europe).

They are also the controls for the base A/C units installed in world cars. if you do have a Sanden compressor then it is likely that you have an aftermarket install. MB didn't install any Sandens, they would have used a GM A6 on a V8 up till around 86 when they started to use Nippondenso compressors.

I agree that the Diesel Kiki compressors are a bolt-on replacement (for Sandens) and are great compressors. I would never use a rebuilt especially on such an inexpensive compressor. I pay less than 200 for new ones so I'm sure they can be had for a better value than that rebuilt price.

I discussed the panels questions with my mechanic. I do have a hang-on conversion system. The A/C hoses are of later design and do not leak R134. I do have a sanden compressor.

The Plan: To save shop labor costs I will be disassembling the dash to allow more complete searching for the A/C leak with dye and the sniffer. I will have the idle head pressures and compressor function checked. I will concider changing to a Kiki compressor and a parallel flow condenser and going back to R-12 depending on where the leak is located. If the evaporator is the problem then I might try the condenser replacement and installing the US spec evaporator housing.

I appreciate all the info, advice and suggestions.
Jim