I took my car to my MB certified indy shop today because my A/C is cold on low and cool on high,I want ice cold! They evacuated it and recharged it (with dye).It had no leaks and the machine indicated it was operating as it was intended.My indy told me that because the evaporator is copper instead of aluminum and we are in such extreme heat and humidity( South Florida) that this was the best I can get unless they exchange my evaporator for an aluminum one, which they did not recomend. Anyone hear of this before?

Are you running refrigerant 12?

Eighties Mercedes cars are not known for their great AC performance, even from the factory with refrigerant 12. Convert to 134a and all bets are off.

Cold on low and cool on high suggests a capacity problem and not a problem with the heater circuit.

Check for dirt in the condenser and radiator, and that your fan shroud is properly attached. Also you may have a dirty evaporator preventing flow there. The old models did not use a filter in the cabin air path, so the evaporator collects the dirt. If the outside mechanicals are fine, extract and weigh the refrigerant to determine if you have the correct quantity.

The indy evacuated and weighed my r134 and it was a 1/2 ounce off.My a/c is ice cold at 80mph on low and cool on high.I can tell the temperature change when idling or driving around the city compared to an 60 mile road trip.I have tinted my windows and replaced the monovalve last weekend.When I was doing the monovalve I dropped one screw and ended up taking out the windshield reservoir,battery and battery tray to find the screw and I am glad I did.I got the shop vac out and vacumnned out years of leaves. I guess it is what it is.I live in a hot and humid climate.I do want to make sure the flap closes to make sure no fresh air comes in when I hit recirculate.

So you are running 134a. Are you still using the R12 condenser?

Matt not sure about the condensor?I did not own the car at the time of conversion. I guess they are supossed to be different?

How can I tell?stamped part number?

Good question, Gummy. It's fairly easy to identify the old tube-and-fin condensers that were used for R12. The difference between serpentine and parallel-flow condensers is less obvious, as they both use flat tubes. You may be able to tell by the side tanks. A parallel-flow condenser will have side tanks that each cover about a quarter of the lateral tubes.

so you are running 134 in a 12 system.134 is only 70% as good as 12 so they had to grab more efficiencies with the hardware[eg. parralel flow condensors].one thing you can do is to remove the aux fan and wash down the condensor with mag wheel cleaner so as to clean the black paint off the condensor tubes.this will give you about 20% more effic there.then you need to empty the glovebox and take out the black rectangular plug at the rear,now you have access to the fresh air door.with system switched to full cool take a long screwdriver and push on that door to see if it will move toward the firewall.to get full cooling it needs to be completely closed.if it's not call me and i will explain how to fix it.

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David S Poole
European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
http://www.w108.org/gallery/albums/A...1159.thumb.jpg

I had the same problem with my 84 500SEL. I did 2 things that helped a lot but was very time consuming. First, I cleaned the condensor with Mag wheel cleaner. (the old type, not the new and improved kind that is "Clear coat safe). I cleaned it until it was shinny bare metal. Next, I removed the blower motor and using a mirror, I looked at the evaporator. It had a lot of leaves and junk packed in there. Using a refregator brush (Wal-Mart has them) I would brush and them vacuum, look, brush and vacuum, look, etc, until I got it as clean as I could. I then blew it out with air as good as I could. The evaporator is about 22 inches long and 7 in high and you can't see it at all without a mirror so this process takes a while.
The other thing that I could have done was remove the evaporator and I am sure that would have been better BUT the labor guide gives about 20 hours to R&R the evaporator so I went with the first process of doing it in the car.
The results were a much better cooling system. By the way, I was using Freeze-12 freon.

Paul

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84 500 SEL (307,xxx miles)

Instead of the mag wheel cleaner, you could try condenser cleaner. Seems like it might work a bit better. Maybe not.

Thanks for all of your help!!! We are going to the Bahamas tomorrow morning and I am going to end up working on the car,sounds like fun.

Hi just an idea for you to consider.I have a 1987 300e which had been converted to R134 before I bought it and the air was never very cold (I live in the tropics) Just a couple of months ago I had it vacumed and filled with R12A which is a propane/butane mix this dropped the temperature coming out of the vents by 10 degrees.

The wife got home from work,opened the hood and have the tube and fin condensor.Should I get a new condensor for r134?

You would be happier with a parallel-flow condenser with 134a. Unfortunately, there probably is not a direct fit condenser available. If not, you will need custom lines which can add to the expense.

Do you know what oil is in your system? If it is miscible in r12, I would go back to that. It would be a lot cheaper than to fit a parallel-flow condenser.

I don't recall if Florida is one of the states that bans hydrocarbon refrigerants. If not, that may be another option, depending on the oil used.