Hi I have a strange AC Problem, and after spending some time to search thrue the forum and and not able to find the answer...here I am.

I have '84 300D Turbo. My AC just stoped working a few weeks ago. AC Compressor Clutch will not engage. I have checked fuses. I have power on one side of teh drier but not other, tried to jump the wires on top of the dried, that did not start AC. Tested if there is power to the clutch..None. I do not know where else to look and waht to look for. Any ideas??

Also, I have no air blowing from the 2 middle vents....are the problems related?

Any help would help, as I live in Texas and summer is almost here

You need to start by checking pressures.

Good luck,

Go see Zack at Zack's Auto repair. Located on FM 78 in Kirby. He is great on older Mercedes climate control systems. Fair prices too! He did a super job on my 300E.

You need to start by checking pressures.

How can I check teh pressures when AC Compressor is not on??

Also where is the relay located for AC in the car and how can I check on it (or should I)?

The same way that you do with the a/c compressor running. You connect the hoses to their respective fittings and read the pressures. In the case of static pressure you only need to connect one hose.

If you have about 80 psi then you have enough pressure that the high pressure switch should be activated. If you have something less than about 75, then you have a low charge.

Seeing if there is a charge is always the first step in troubleshooting a system in which the clutch will not engage. If you don't take this step you can easily find yourself "chasing your tail."

Good luck,

Thanks Larry. I will try it this afternoon.
I have a question for you. My sytem was changed to 134 last year. Would the pressure be any different or it all should be the same?
If you have about 80 psi then you have enough pressure that the high pressure switch should be activated. If you have something less than about 75, then you have a low charge. Do I test low presure side?

Statically the pressure will be about the same. Dynamically, the 134 will build higher high side pressure than 12. In fact, you need to see that you do not overcharge with 134 because the high side pressure will sort of run away and get too high.

Good luck,

Larry, you are AWESOME!
My system was totaly empty....the moment I added a bit of refrigerant my compressor came on.
I just need to find a leak in the system now.
Any suggestions?

There are several methods for finding leaks and they all involve purchasing supplies and/or equipment. I like to start with UV dye. You can buy the UV dye for 134 systems at most auto supplies. It has an ounce or two of oil, UV dye and several ounces of UV dye, so you just add it like any other can of refrigerant.

Since you have a converted system, you must read the fine print and make sure it is for Ester oil systems. Once you charge the system, if the leak is REALLY bad you can see the dye with the naked eye, but it is best seen with yellow shooters glasses and a black light.

Since it's 134, I would go ahead and charge it up, putting in a can of UV dye first. You can buy a leak detection kit with a black light for not too much money, or maybe find some kind of black light to use.

Start looking for the leak at the compressor shaft seal, any joints and maybe the condensor. If you don't find anything there, then drop the passenger side underdash panel and check the expansion valve. If you don't see a leak there, get it cooling enough to drop condensation on the floor and shine the black light into the condensation water. If there is UV dye in the condensation water, then the leak is your evaporator.

Good luck,

Thanks Larry
I'm a process of charging the system now....and I got a can of dye to put in it.
I will let you know how it goes..
For some reason my 2 midle vents do not have any air comming out of them in any settings on climate control panel. First I thought that it might be because my AC did not work, but now that it's almost fully charged they still do not put out any air, I'm thinking there is a problem....
Any ideas??
Thanks

Nop did not find any obvious leak in the ac system. I think it might be leaking out little by little thrue the new fittings for 134.. I will have to keep an eye on them.

Any suggestions on why my middle vents do not put any air out.....well there is barely something comming out from there. They used to work just couple of weeks ago, before my ac went out???

Larry mentioned the basic areas of the 123 system to review. You have a 20yo Texas car and the system may not have had the O-rings replaced when the conversion was done.

Other places to check: The receiver dryer and the pressure switch. The 2 O-rings that connect up the condensor. The back of the compressor (2) AND just above that is another O-ring that can leak. The hi side hose connection behind the alternator (1).

You also need to check the lo and hi side schrader valves (1 each). Those can leak.

Lastly, the hoses need to be checked primarily around the metal fittings. At 20yo the rubber can develop leaks near these areas. Also check the hoses carefully under the battery tray. Sometimes a leaking battery can eat away at those hoses.

Lastly, you have sprung a leak of R134 (and the OIL) you just can't add more R134 without adding some of that oil that leaked out. Here is where my experience ends and maybe someone can pipe up and suggest how much oil to add in a sitution like this (once the leak is found).

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

I'm not that familiar with the 123 automatic climate control so I can't offer much help with that part. I think there are some vacuum diaphragms that control the center vents, so make sure that is okay.

If your fittings are leaking are they aluminum? It is common for people to get the junky aluminum fittings at the parts store. You should get steel ones. They have sort of a brass looking coating on them. You can get them online and I have seen them sometimes at Pep Boys.

Good luck,

Thanks guys for all your help.

Now, does anyone has some kind of vacuum diaphragm for the center vents on 123. I still need to get those vents work, and I do not want to break them as some guys did (I've read).
Thank you all again

There may not be a problem with the center vents. The center vents on my car rarely come on, but I know they do work. They only work under certain conditions, such as high demand air conditioning. The ventilation system gives priority to demisting the side windows over comfort. This is part of the MB philosophy of safety first.

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95 E320 Cabriolet, 159K