am having a hard time finding information on W115's. The AC just recently went out in my 76' 300D and I'm not exactly sure where to start the repair. Other than this the car runs flawlessly, anyways The previous owner replaced the York with a Sanden model U-9120. The only time that the AC "blows" is when the car in motion, and its not cold air. Obviously there is a problem I just don't know where to begin the diagnosis.

I am about to start working on it in the next hour or so, I'll continue adding details to this thread as I discover them. I am a novice with this vehicle and especially the Sanden. This car is my first step into the world of "classic" Mercedes cars and it would kill me to here that this problems indicates thousands of dollars worth of work. Any help would be greatly appreciated!


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There is an AC thread in my signature...
a good place to start...
Find out if your system has R12 or R134a
You are going to want to put ' gauges ' on it...
to determine if it is partially charged or fully charged and some other problem exists..

it says on the compressor.. R12...but that might not be true this many years later..
so look for new tags which say a conversion has been made... AND look for the different looking access points plumbing..

If it only cools when traveling forward... sounds like your ' air across the condensor' is lacking when not moving forward..
so if you have a fan clutch.. check that.. if you have electric fans check those for operating correctly...

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

The pic of the compressor label says R-12, so hopefully this is correct. The first step is to turn on the AC with the engine running and visually see if the compressor clutch has engaged. If not the likely cause is electical (fuse, etc.) or a faulty compressor clutch, or low on freon. AC works involves the use of specialized tools and equipment plus appropriate safety procedures. You might be money and time ahead to take the car to an AC specialist for diagnosis.

Yes, if you have someone you can trust to diagnose the AC system that is a great idea...

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Update 1 fuses good. Sanden clutch not moving.


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First of all, don't let the "Mercedes" part throw you off. AC is AC, pretty much though there may be specifics on wire routing, pressure switch type, etc. that are specific. So basically, any AC shop worth their salt ought to be able to sort this out for you. Living here in the SE, AC is a critical function and pretty much any decent repair shop does a good job with AC. Worth asking friends, co-workers, etc. for their experiences with any given shop. Because specialized equipment and skills are needed, I shop AC work out to a friend's shop. I simply would never do enough of it to justify the equipment unless you want to make it a side job (a friend in MI did that).

Dan

The green knob vacuum elements and switch over switch need to work. Does the Ac blower motor work? The heater motor and Ac motor are not the same.

I once had a long talk with an associate who owns and operates an A/C shop about converting a Mercedes to Sandlin. He feels the standard R4 compressor is the best and he said Mercedes owners are not doing themselves any favors by modifying the A/C system in anyway whatsoever.

Of course, that is just his opinion; that said the guy has worked on thousands of different vehicles over the years and has pretty much seen everything out there.

This forum is a goldmine of information and assuming you are mechanically inclined and understand the ac involves high pressure and can take the appropriate steps with the right equipment (guages, freon, vacuum pump,air compressor..) you could do it yourself but if you are not comfortable with any of that you may just head to a good ac shop. Having said that, for my 240D, the ac was inoperable when purchased, "just needs a can or two" like they always say. If you don't know whats been done to the ac, you may just start from scratch like I did. I figured it was due for a flush anyway.

I purchased the o ring set,r12 guages, a good synthetic ac oil, freon, expansion valve, dryer, two cans of ac flush and:
-confirmed the compressor operated for a second by jumping the low pressure switch
-flushed the system with ac flush, followed with lots of compressed air.
-replaced "O" rings throughout
-replaced the expansion valve just for kicks and grins
-added oil to the condensor, dryer and evaporator (small amount forget the exact level see shop manual)
-replaced dryer
-pulled a vacuum test (at the time I wasn't aware a pressure test with C02 would be better)
-added freon (got a case of 12 at a farm auction for $60)
-cleaned/flushed evaporator with water and scrubbing bubblies. (Check ac drain first)

After all that it worked great this summer. Before attempting though, I would recommend just searching and reading this forum and you can get some idea of the work involved in each step it's not as easy as it sounds!
Frank