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Old 07-25-2005, 05:59 PM
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Join Date: Jul 2005
Location: Lansing, MI
Posts: 108
134A conversion help

I searched the threads for help on this and mostly found only rantings of whether 134 or r12 was better. basically I know I must have a leak somewhere and want to convert it to 134A. I'll need to know which hoses and o-rings, ect. to replace as well as what to use to vaccumm my current system. If you think you can help, please feel free to contact me directly or with a simple reply. thanks

'86 300E (241K)
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Old 07-25-2005, 06:32 PM
BamaMB's Avatar
Ima fix'n to
Join Date: May 2004
Location: Birmingham AL
Posts: 110
Try for info on vacuum pumps, gauges, parts and o rings. Also lots of good info on basic A/C system repair.
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Old 07-25-2005, 08:06 PM
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Join Date: Apr 2005
Location: FL
Posts: 71
minimum conversion--fill system with 134 to chk for leaks. fix leaks. evacuate system. repl receiver-drier and o rings at that connection. vacuum system and recharge with 134a and at least 2 oz of oil.

to do it correctly to last for a long time--fill with 134 to chk for leaks. note pressures on guages. if good, you can reuse compressor if it's not the leak. make note of where leak is. disassemble all hose connections (condensor, compressor, rec-drier, expansion valve, evaporator). flush all lines, remove compressor and turn upside down to drain overnight. reassemble with all new o-rings, new exp valve, new rec-drier, the two switches on the rec-drier. vacuum system and recharge with r12 or 134a and the appropriate oil.

not a bad DIY job if you have a/c gauges and a vacuum pump and know how to use them.
"the simplest answer is usually the correct answer"

1991 190e, 2.6 (helga)
91,000 mi
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Old 07-25-2005, 08:45 PM
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Join Date: May 2003
Location: Vancouver, B.C.
Posts: 52
R134 conversion

I did the R134 conversion on our '89 190E 2.6. It was a real chore, and I encountered nothing but hostility from the people that I had to rely on for the actual evacuating and recharging. Fortunately, my non-dealer parts guy knew everything.

I had to replace the compressor and a big expensive hose (which incorporates the fuel cooler and is only available from Mercedes), because they apparently were leaking. I don't trust the guys who said so, and I have a lingering feeling that I may have replaced parts that were fine.

You can buy a universal kit (R134 comatible o-rings, port adapters, and a compliance label) almost anywhere. I have even seen them on e-Bay.

You will need R134 compatible oil. The aircon guys will want to add this, at great price. However, by the time they get to the car, you will already have had to add it to the compressor. You can't run the compressor without oil, and they are adding it while the engine is running.

You need to get the compressor out, to get the mineral oil out. Just turn it upside down and pour it out. You cannot do it on the car. This is a real job. It involves removal of the bumper, radiator and condenser, alternator belt and tensioner, water pump, and power steering pump.

Then, the compressor is held in by allen-head bolts which have been there for 20 years. That is when I bought a dremel tool, to cut off one last allen head after the hex hole was rounded.

Pour the old oil out, rotating the pump shaft. You don't need to get it perfectly clean. Apparently the old oil just sits there and does no harm. The new oil circulates with the coolant. But if you leave it all in, there is too much liquid in the system. Add new oil to the compressor. The quantity is a little less than specified for the original oil. I think 80%, but I don't remember for sure.

Once the oil is in, everything has to be sealed up tight. The R134 compatible oil absorbs water, which will really screw up the system, by evaporating, freezing, and causing corrosion. Even before then. you need to plug every hole, all the time, to prevent contamination.

Some say that you can leave the old o-rings if you don't disturb them. I did not believe it. Every joint has an o-ring, and the kit has all you need and many more. Once you are in there, it is very little extra work.

Everyone says replace the receiver drier and the pressure switches attached to it. Also the expansion valve, which is a different size for R134. These are relatively inexpensive parts. One of the switches is a high-failure part (according to my parts guy).

There are dire warnings about failed compressors and how they spread aluminum shards through the system. I found nothing.

The condenser has one inlet and outlet, but internally it splits into two parallel tubes. That means that, if one is blocked, you can't blow it out. All the air goes through the other tube. Fortunately, mine seemed to be as clean as a whistle. There was not even oil in it.

The 190E has three ports. The kit had enough adapters. You just unscrew the schraeder valve from the existing port, lube the o-ring, and screw on the adapter, which has loctite already on it.

My system cools quite well, now. It probably cost me close to $2000 Canadian, in parts and extortion-level labour. It would have been a lot worse to have it done professionally. Half that was the new compressor, which I am not totally convinced that I needed. I have since seen compressors on e-Bay for a lot less than I paid.

Mine was a worst-case scenario (almost). Two expensive parts needed to be replaced, and I was stuck for a day getting the last allen-head bolt out. You may get away with the kit, receiver-drier, two switches, and the expansion valve. It is still days of work.

You really need the air conditioner, at least in our climate (west coast rainy). It is an essential part of the windshield dimister/heater. One winter without it was enough.

Good luck!
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Old 07-25-2005, 09:02 PM
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R12 is coming down in price while R134 is going up fast. There is just no valid reason for converting an R12 system to 134 given todays refrigerant prices.

If you have a leak that is so bad that the refrigerant is going to come right out, then it is enough of a leak to find with an electronic leak detector. If you don't have one, a shop will check for you for a pretty low cost.

Statistically a converted system lasts about two years. A few years ago when R12 cost as much as $50 a pound, it seemed to make sense to convert. Now with 134 at $8 or $9 a pound and R12 at $14 a pound, where is the logic in spending a bunch of time and money to convert?

Best of luck with it,

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