[R129 SL] Another air conditioning question

[Jan Kuylaars]

George.
 
I am not a expert in AC, but basic working is that the compressor
compresses the gas to fluid and the fluid is giving of the heat that is
produced by compressing.
The front radiator is for cooling the heated fluid by passing air while
driving, or by air stream with the electric fans, during standing still.
The heated gas is pumped to the receiver drier to take out the moister.
After the drier there is a pressure control switch for shut down the AC
if the pressure is to low and a other for running the electric fans if
the pressure is to high.
 
If you system is not completely filled, you can see air bubbles in the
glass from the drier when the compressor is running. 
When you see no bubbles there is to less or no refrigerant.You can check
on the compressor. There should be a different in temperature in the
inlet and outlet
After the compressor stops , and there is a clear vision in the glass,
there is to much refrigerant in the system.
If the amount of refrigerant is perfect, the refrigerant should foam and
then stay clear after the compressor stops.
 

>From the drier the fluid runs to the evaporator inside the car , where

the fluid can expand to gas again, and for this expand the gas needs
heat.
The evaporator takes the heat from the room and the room becomes cool. 
 

>From the evaporator the gas is flowing back to the compressors low

pressure side, where the gas is compressed again to fluid and the
process starts again.
 
So as long as your car is driving and the radiator will be cooled there
is no problem.
When your car is standing still and the engine temperature is climbing
the problems starts;
 
There are in mine opinion two possibilities, I am not for sure , but I
am are trying to think with you :
First there could be  a failure in the basic operation, and the second
one is electronic problem from the regulation of he AC.
 
Lets start by the first: if your car is standing still and your electric
fans are not working, the fluid is not been cooled and the heated fluid
results in higher pressure .
Also there is a higher temperature in your evaporator. There is
expanding from the gas but it don't needs a lot of heat for this because
the temperature already is high. The result could be that the emission
of heat out of your car to the evaporator is gone. So no cooling.
This could be resulting in a spiral. After the pressure comes too high
the system shut down or the refrigerant will come out the high pressure
security valve.
Result to low refrigerant and not proper working of the AC.
 
Possible failure could be the fans, the fan control, the pressure switch
or the expansion valve which are not good operating with higher pressure
or heat.
 
Then there is a possibility for electronic failure , like the Italian
college told; The measure of inside temperature and outside temperature
in combination with the temperature from the engine. He told us to fix
this problem with a resistor placed in series with the engine
temperature sensor. Read the earlier messages.
 
Also there can be a failure in the circuit itself.
When you wish I can send you the electronic circuit diagrams and the
diagnose procedure.
 
Greetings from the standing still Dutchmen with damaged gearbox. 
 
I discovered on the bill from my garage that beside replacement from the
starter and the steering house, they replaced the rubber pipe from the
gearbox oil cooler because it should leak a bit. After that I only drove
40 miles before my gearbox looses oil with pump noise and burned oil on
the exhaust as result.
I must check if the rubber pipe is come loose, and maybe they are the
reason of no just oil level or other damage.
But then I have a problem if they are willing to confess and pay for the
damage.
 
Jan.
 
 
 
 
 
 
 
 
 
 

-----Oorspronkelijk bericht-----
Van: r129list-bounces at mbcoupes.com
[mailto:r129list-bounces at mbcoupes.com] Namens George Jenner
Verzonden: donderdag 12 juli 2007 15:59
Aan: SL Mailing List
Onderwerp: [R129 SL] Another air conditioning question


I have been experiencing a perplexing problem with my 1996 SL500 air
conditioning system.  I have the means to check the pressure on the
system and have noticed that when I first start the car the air
conditioned runs normally cold.  As I drive and the car heats up the
system runs normally, but if I turn off the engine (to gas up) and the
out door temp. is hot (in the high 90s) when I restart the car the air
conditioner is no longer running cold.  This has led me to check the
system pressure at various engine temperature stages and the pressure is
in the normal 40 - 50 range when the system is cooling normally but
jumps to 100 + when the engine is hot and the system no longer is
cooling.  I do not think I am loosing coolant but need help to locate
the problem.
 
Has anyone any idea of what may be causing this problem?
 
Thanks, George

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