Yes, the oil travels around the system and some rests in the low spots, including each of the components of the system. So that would be natural and not an indicator of too much oil in the system.
I do not know about the pressure results from overfilling,, have not seen anything printed about that... only this....

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I want to share an article I found in the Automotive Cooling Journal which discusses techniques of testing for over/under charging of oil.


http://www.narsa.org/acj/archive/acj200105_ac%20focus.pdf

http://server1.aircondition.com/dsmobileac/

This is the website with compressor oil capacity information.

This weekend I thoroughly flushed the system: evaporator, condensor, and hoses. I first flushed with air, then with paint thinner, then with a/c flush, then with brake cleaner, and finally with air.

I put 6 oz of ROC oil (universal refrigerant compressor oil) into the system:
3 oz into the compressor
2 oz into the condenser
1 oz into the evaporator.

With a new receiver/dryer, I evacuated the system for 3 hours.
I charged the system with 12 oz of Duracool (16.5 oz recommended).

I also fixed the blend door that was not closing.

At 103 degrees and 70 mph, the middle vent temperature was 59 degrees. This was the best performance so far. My 89 Pontiac Grand Prix would put out about 52 degrees under these conditions. Considering the undersized A/C system in the Mercedes, I think my A/C is the best it can get.

At this point, to get any cooler, I would have to change the condenser to one with double the capacity like the one used on a 380 SE.

59 degrees would not be cool enough here in the Texas heat. I finally got my system thoroughly flushed and recharged after installing two new compressors (the first one failed). At cruising speed, I get an indicated 33 degrees, 40 while in stop-and-go driving. My interior is black and seems very difficult to cool down, but this A/C is doing an admirable job. THIS is why I went back to R-12!

__________________
Matt
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1995 E300 Diesel (Die Blau Frau)

Zoonhollis,

I don't think my W126 300SD is capable of cooling below 59 degrees under those conditions. Your 85 300D-T has a condenser twice as large as the one I have on my 300SD.

Ok, maybe I missed something somewhere...

If 16 oz is recommended, why did you put 12 oz in ?

Usually the way in which Evacuation is judged is by the amount of vacuum you pull.... ( plus the time ) .... since vacuum machines are of different abilities ( and condition ).... Do you know how many inches of mercury you were pulling ?

leathermang,

The reason why I did not put the recommended is because the pressure with 12 oz was 65 psi on the low side at idle. When I revved the engine to about 2000 rpm, the low side pressure dropped to about 25 psi. I do not understand why the system acts like this. From what I understand, the pressures on the low side increase when the engine rpm increases.

I have basic equipment. I have only a single low side gauge. My vacuum pump is a refrigerator compressor. I had it tested and it had a vacuum of 26 in hg at 2000 ft above sea level.

When I evacuated the system, I found leaks around the TXV. I tighted the fittings, and things were fine.

If you had a high side gauge, which I would recommend, you would see the high side pressure drop too because of the effect of inproved heat exchange effect due to the increased air flow through the condenser.

__________________
Jim

Mercedes Man,

Yes indeed it is IMPORTANT to monitor high side pressure. Without seeing both you are flying totally blind.

That said, your description of your low side behavior could possibly indicate system blockage. Without monitoring pressures on both sides you cannot confirm this.

Good luck,

How much does a High pressure side guage cost ?

leathermang,

There's a good deal on a R134a gauge set at Harbor Frieght. It has a sight glass and sells for $65.

LarryBible & engatwork,

Without a high side gauge, I tell you that the condenser on my 1984 300SD is too small. It is a single row. The sticker on the car says to charge the system with 2.9 pounds of R-12. The system is so small that if I did that, the system would be overcharged.

I found a picture of the condenser that goes in my car. In the picture, you can see two rows of coils. Mine only has one row! This isn't enough capacity to cool a compact car.

The condenser is the original in my car. How could they put the wrong condenser in?

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Mercedes Man,
Your best bets at this point in time are 1. buy the high side guage, 2 buy the very best AUX FAN to put in front of your condenser...THE primary limiting factor in producing cold air in our autos is AIR FLOW ACROSS THE CONDENSER ( no matter what size it is ).

I have an electric engine fan. I also have two condenser fans: the original and a Honda Civic condenser fan along side the original. The Honda fan blows more air than the Mercedes fan. They all run at the same time when the air conditioner is running. Along with blower, they really suck down power.

I was looking at condensers in the junk yard today. Almost every car has two rows, except for a 1981 Toyota Corolla which has one row. I used to own a 1981 Toyota Corolla, and it did not cool well at all since it was brand new.

So, why doesn't a W126 diesel have a double row condenser? Don't all the gas W126 cars have double row condensers?

Well, you seem to be in good shape on the fans then... so that puts you back to number one.... get the high side guage so you can go back to your systematic diagnosing of the rest of your system's condition.