My mechanic just called me and said my A/C system wont take a charge, that hes not sure what they are doing wrong and that i may have to take it to the dealer for this service.
The system is the old R-12 and the compressor is still working and the system worked beautifully until 2 days ago when the air slowly became less cold. Its still noticeably colder than the "EC" setting, but not cold enough.
There is limited info. on the A/C systems on these W123 cars so please help me! I dont want to take it to the dealer. Ive got a 1983 300D, why wont it take a charge?

I have had instances where the shcrader valve was not depressed fully by a set of the newer, anit-blow back valves on the gauges.

In this case, I just use an adapter off of another gauge set.

Be sure he is charging from the low pressure port.

__________________
Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS

Thanks benzmac,
Im going to try another guy tomorrow, ill remember your comments. These guys didnt seem to have a clue. At least i wasnt charged for it.

Brother of The Benz, Jeep Boy
In reading your post how the discharge air slowly became warmer and that the system would not take a charge; sounds as if the compressor does not have any suction, the low side pressure is too high.
Using R-12, the low side pressure should be approximately 32-34 psig.
As the compressor hasn't the ability to pull that pressure, the evaporator temp rises.
If the valves in the compressor are not closing to create this suction the freon can not be drawn into the system.
If you can, a simple method to test the compressor is to use 2 wooden flats across the suction hose and clamp the hose off using a "C" clamp.
This will make the compressor pull max suction pressure.
If no suction then you've found your problem.
Then there's the expansion valve if the compressor checks OK.
If you had a restiction on the low side the pressure would be a it's minimum, and if on the high side at it's maximum.
I hope all of my rambling on hasn't put you to sleep.
And I hope I'm totally wrong for this week I had to replace my compressor.
Happy Trails Beep Beep from The Spiderman in Houston!!!

[Edited by dlswnfrd on 06-14-2001 at 10:43 PM]

Hey Spiderman,
Ill try your advice tomorrow.
If i clamp the hose, how will i know if there is no suction in the compressor? If there is no suction, then the compressor is bad. Sorry for the confusion. Ill try it out tomorrow morning.

If your tech can't figure this one out, you definitely need to find another tech.

Good luck,

Im going to take care of this myself and convert to R-134 today. The system is empty the second tech said, perfect opptortunity to convert, the compressor still continues to run.

I just got through retro-fitting the system to R-134a, it took all 3 cans plus the oil but the A/C is still not cold, and the compressor still clicks on. My guess is that it needs a new compressor. This car has a GM sticker on it. Whats a fair price for this work? Im really scared now.
Anyone? Thanks
brett

it doesn;t matter how many pounds of R12 you pump in, if you have a bad hose, you won't hold a charge.

Brother of The Benz, Jeep Boy
As Larry replied, if your tech can't figure this one out, change techs.
If you were able to install 3 cans of freon, the compressors suction MUST be operating.
As how to tell if it is, you have a manifold gauge set that you used to charge the R-12 system.
You say you have a GM type compressor?
Does it have service valves?
If yes, you don't have to clamp the low pressure hose, just close the suction side service valve and see how much suction it has(inches of hg.)
Now you plan on converting to R-134A?
If it won't cool with R-12, it won't with R-134A.
You need to do some serious trouble shooting and keep notes and/or get some experienced help.
Happy Trails Beep Beep from The Spiderman in Houston!!!

OK Spiderman,

Yes it did take the 3 cans of R-134a easily, plus the oil, but no cold air. Is there some sort of cut valve on the compressor. Ill look today. So as of right now, my system is full of R134a, compressor is operating, but no cold air.
Do i use a guage set with the R134a refig. as well?

Brother of The Benz, Jeepboy
I don't know what size A/C unit you have, but my 1987 300E uses 2.2 lbs(35.2 oz) of R-12.
In retrofitting to R-134A you decrease the capacity by 15%.
My system then uses 1.87 lbs of R-134A or approximately 2 1/2 12 oz cans.
If you installed all three of the 12 oz cans or 36 oz total into your unit, you may have it SO OVERLY charged that something has to give and it can be quite costly and dangerious.
Determine the proper amount of R-134A required.
I may require emptying the system and starting over.
You won't have to had additional oil, although you may consider adding the dye/stopleak additive, and just the proper amount of gas.
Here's hoping you do your homework.
Happy Trails Beep Beep from The Spiderman in Houston!!!

My system takes 2.6 lbs of R-12. So using all 3 of the 12oz. cans dosent seem to far off if you decrease it by 15% like you have recommended. The last can i only used 80% of it id say. Ill have to have it checked out by a third tech now. The second tech said it was completely empty and should convert it over to R-134a. The first tech said he put 1 lb of R-12 in but his gauges always read 0 so he concluded it wouldnt take a charge.

I don't know what you have done but I would like to add my experience. I purchased my 82 300D and the air did not work, no compressor. I by passed the pressure limiter switch to see if the system was low on coolant, sure enough it was. Very little pressure is required for this switch to function so I knew my system was flat. I charged the system and found the components to function, one line hot one cool, yet cabin temp air was still very warm to hot. I then removed the opperating portion of the mono valve to verify it opened and closed on command which it did but the rubber diaphram was shot so I ordered a new one. When new valve body was installed the cabin air was very cool. In subsequant reading I found out Mercedes uses heat to manage temperature in cooling mode and the refridgerant to manage temperature in heating mode. These cars do not use external air to "temper" the system. Once I replaced the valve the cabin air was cool. Perhaps this will help you, I hope it does.

Rick

I forgot to add this... If you clamp off the rubber hose going to the mono valve you can quickly test if the coolant is having an effect in the cabin.

Rick