Can anybody please advise if the valve on the compressor (on 1986 300E with M103 6 cyl. engine), is low or high pressure? Also I have bought a R12 to R134a conversion/recharge kit and the instructions state that you should just add the new ester oil and that the existing oil does not have to be removed because it would just sit at the bottom of the acumulator. My system has a leak and at this time has very little R12 can I just evacuate by pressing the high pressure valve and letting the remainder small amount of R12 gas hiss out??? Has anybody tried this?
By the way R12 is illegal here in Canada – any shop using it is subject to loosing their license, fine and up to 15 years imprisonment. I know it’s silly to do this in Canada while our southern neighbors are still polluting but this is where I live.

I have cut and pasted part of the FAQ instructions --
9. Do I need to remove the oil that's in the system? Is the old oil compatible with the new oil?
No. The residual mineral oil left behind after you evacuate a R-12 system will not mix with the new R-134a refrigerant. That is why we add Ester Oil, because it will mix with R-134a, lubricate the system components and is compatible with the residual Mineral oil.

The mineral oil just collects in a low place in the system (such as the accumulator), where it stays, until it is removed at some later date during future maintenance or repair. The mineral oil does no good, but it does no harm either. It's just there.

Take the 134 conversion kit (I call them suicide kits) back to the store and get your money back.

134 prices are taking a big hike this year, while R12 prices are coming down. In the long term you will cause many problems for yourself by doing a blind conversion with one of these kits. Even doing a correct conversion including changing the r/d, flushing the system, doing o-rings and evacuation will cost MUCH more than simply doing it correctly with R12.

This is not to mention the fact that even a PROPERLY done 134 conversion will result in a 15% loss in cooling capacity.

If you want to know more you can do a search. There have been untold volumes written here on this subject.

Good luck,

Since the poster is in Canada, he does not have access to R-12. Our northern neighbors completely banned R-12; he has no choice but to convert.

That said, I'll second Larry's opinion. You are very unlikely to get good results with a so-called "death kit." R-134a will be sufficient for a Canadian summer, but you need to do the conversion correctly - flush the system, fix the leaks, recharge correctly.

And no, you cannot just release the remaining R-12 from the system. 1) It is illegal to do so. 2) The system must be evacuated before charging - any air inside the system is a very bad thing.

- JimY

Thank you for responses – but if I decide to use this suicide kit – please confirm that the low pressure valve is the one on the compressor body – I believe that the valve on the top large hose going to the firewall is also low pressure but I just want to be 100% certain. ---Also is the compressor pressure not sufficient to blow out the little if any remainder freon out the high side?

Have done it the proper way, a couple of years ago, for my Saab and it the AC still works great. However the final bill was about $800 while this kit just cost me $49.00. I think it's worth a try and if it doesn't get me through a season well then we'll see or I just wont drive it on 30 + degree days.

I have a 1992 300E. The system was converted to R134a by the prior owner in 1997 when they had the evaporator replaced.

Last year I replaced the compressor, expansion valve and reciever/dryer and charged with R134a. The system works fine. I'm not sure but I recall the center vent temps would go down to about 40 degrees with ambient temps in the high 90 degrees. I live on the coast in South Carolina and it's very humid here. So far so good. I guess I'm lucky my system works great for now.

R-134a can work reasonably well in the 124 chassis if all the components of the system are in good condition. I used in my '87 after replacing the evap, condenser, and compressor. It handled Dallas heat without too much trouble. Of course, curiosity got the best of me so I evacuated and went to R-12 (after determining the system was leak free...). And R-12 does work better - faster cool down and slightly lower vent temperatures in the end.

Back to the original poster's question. I actually don't know whether the valve on the compressor is high side or low side, never messed with it. The valve on the line up by the strut tower is indeed the low side. High side valve is down by the fan belt, near the compressor pulley.

You will most assuredly get very poor results if you release all the R-12 and then charge with the death kit. The a/c system must have only refrigerant inside it - no air, and no water vapor. To achieve this, an extremely deep vacuum is pulled on the system prior to charging. To put it bluntly, if you let air into the system, you're screwed. It won't be cold, and it will be damaged.

In the U.S. it is illegal to add R-134a to a system containing R-12. Don't know what the law is in Canada.

- JimY

Thank you - will just take it to shop for estimate and if it's too high will make this 300E my "non hot days car" --

or some other 3rd world country that doesn't care about one vehicle's worth of R12, that most likely already leaked into the atmosphere unknowingly. The law isn't really against releasing the R12, but knowing about it. Just goes to show that there are no laws against being stupid, although if there was, you wouldn't need a bunch of other laws. So, if you tear apart your old AC without doing any research at all, you should be safe. I can't see the Government actually locking someone up for doing something once that junkyards did for years and are still doing. Oh no .. just realized so please keep this confidential or maybe they'll come after me for ripping off that tag on my mattress.

Changing the items I changed was not that big a deal, if your pretty mechanically inclined, now if you have to do the evaporator, that's a pain.

Here is the link to an A/C Forum which a think is excellent. http://www.autoacforum.com/categories.cfm?catid=2

It has easy to follow instructions regarding charging, and pulling a vaccum too. I was helped by this forum last year when I redid my system.