I need to know the process and how much would cost to get a 1982 300 SD Mercedes Benz air conditioning system running with R 134a.
Do I need to change the evaporator and compressor?
Thanks.

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Nyck - TX - USA

From what I researched all you need to do is change the service ports. Here is what I have gathered: evacuate the system and change out all the o-rings. You will also have to add some PAG/POE oil to the system, then add the r134a and that's it. Now there will be many people that tell you to do a flush or that you need to buy new components because r-12 and r134 don't mix. It's a myth. You can mix r-12 and r134 and not have any problems. The molecular make of r134 doesn't allow it to bind with the mineral oil used by r-12 so if you don't add the PAG/POE oil then the mineral oil will just sit at the bottom of your compressor and not be carried through your system to lubricate everything. You will most likely have several members chiming in to either agree or disagree with what I just said, but if you have r12 in your system now then do this: evacuate a little bit out into a container that has r134 and see for yourself. Also mix a bit of mineral oil with PAG/POE oil and see for yourself. I still have the bottle of mixed oils with nothing that was of ill effect. I will caution you this: use protective gear and use a container that is vacuumed. I did this a while back before I converted my system and I mixed the r12 and r134 with both oils and the container began to build pressure from the gases expanding. I was able to reattach my vacuum pump and just cycle the gas. Hope this helps.

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1990 190E 3.0L

Nyck, cost will depend on what you have to start with. If the system is charged but just not cooling as well as you would like it to cool, I would have the system checked for leaks, repaired and charged back with R12. R134 does not work well in these cars. I know. I have been down this road several times. I tried 134, freeze 12, hydrocarbons, changed expansion valves,and nothing worked well enough here in North Carolina. Texas is generally hotter than NC so I don't think you will be happy.

The compressor went bad on my 500SEL and had to be replaced. I flushed the system completely, changed the expansion valve back to the one I took out when I put the 134 valve in. I charged it with R12 that NAPA had at the time. It was $30 per can and it took 4 cans. That was the best $120 I have ever spent. This was about 4 years ago. I haven't even had gages on it since. It works so good that on a 100 deg day, with the temperature wheel set at 22c (about 72 f) we will turn the seat heaters on to help our old bones feel better.

R12 is still available if you look for it. The correct oil for R12 is also still available.

The above is just my experience.

Trivia, R12 became the worst thing to happen to our environment about the same time that Duponts patten ran out. Dupont had the patten on on its replacement, R134.

PaulM

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84 500 SEL (307,xxx miles)

On a 617 SD, do yourself a favor and buy a Sanden conversion kit. The GM built R4 is junk. A member here makes them and others are available. I bought mine from Matt at Klimakit. If you do a search, you can find this information from my thread on the conversion. Dealt with three leaking R4s (even new, not reman), never again.

Early SD W126s have a fairly inefficient condenser also, a puny aux fan, larger water pump pulley, and a small main fan. A poor recipe for A/C, let alone here in Texas.

If you want to stay clutch fan, pick up an M116/7 fan with clutch and it will drop right in. BIG air flow difference which is needed for good A/C performance. A good e-fan swap will work. I have installed a Volvo 960 dual speed unit on my SD, I reused the OE Volvo relay, and a BMW 91°C low/99°C high temp switch to trigger it. Simple, cheap, works great.

The water pump pulley being smaller on the late vehicles increases low speed air flow via the engine driven fan and better cooling. No brainer. You will need shorter belts.

Up to late '88 W126s received a much larger aux fan than the early cars, this started around mid '84 I think. My 11/84 has the larger one from the factory. Plenty of good, used out there to buy.

Your condenser will not work well at all with 134A, it was marginal with R12. You and I are both in Texas, so you need to really, really consider a parallel flow condenser to deal with the R134A. I have a slight hole in my condenser and let me tell you, finding a late '84 to '87 Diesel W126 condenser is a big PITA. I gave up trying to find a good used for a good price and am going parallel flow. Matt at Klima sold me the brackets as he is out of kits currently. The condenser is only $60, you will need to build a new liquid line and high side fitting.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

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