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  #1  
Old 06-19-2003, 12:35 AM
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Question Air conditioning or quantum physics... which is less complicated??

I have been reading a lot of threads on the subject (did a search), but there seem to be many parts and many possible sources for problems. Where to start??

Okay... we have a 1981 300td. It came without a belt on the airconditioning compressor. I knew it wouldn't be as simple as just putting a belt on, but I was hoping. Sigh, it didn't work. THe compressor does not engage. There did seem to be gas pressure in the line (could hear a hiss after turning that little valve). I know that if there is no pressure the clutch won't move and the compressor won't come on. In order to eliminate that as a possibility, my husband hooked it up to a voltage meter, and there is no power going to the compressor at all. I can't see that there is a fuse for the airconditioner. Maybe a relay switch? Or the compresser itself?

I talked to our mechanic breifly about it and she said if it had been sitting any length of time without running, the compressor would have to be replaced. She said not to bother with rebuilt as she went through 3 before finally buying a new one. I checked out the price of a new one, and it's about $600+. At that price we'll be using the 2/60 AC... 2 windows down and travelling 60mph!). She also said we'd need an R134 upgrade kit. (In Canada they try to discourage the use of the other kind of refrigerant because it is bad for the environment. They dont' outlaw it, they just price it out of reach).

I'm not sure if it's related, but I'll mention it in case it is... the heater also doesn't work properly. Or actually the HEAT works, but the temperature setting makes no difference. The only choices are HOT and Burn the Hair in Your Nostrils. From what I've read here it sounds like that could be the monovalve??? Is that a separate problem from the AC issue?

What would be the most logical thing to try first? (and second and third). Someone on ebay is selling 'everything needed for hte AC system from the firewall forward'. It's kind of tempting! But, my luck the problem is on the other side of the firewall.

Thanks!

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Old 06-19-2003, 07:28 AM
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Ok, let's check some easy stuff first. I think there are TWO fuses involved with the climate control. #8 and #14 come to mind, but won't swear to it. Check all the fuses with voltmeter. I have seen them look great and be bad. Next, just for fun, try jumpering the presure switch on the reciever/dryer. That is the device with the glass window in the top of it where you can see the freon/bubbles when the system is running. I think it will be on the right side near the headlight. Just pull the connectors off the switch and short them together for a second with the car set for max A/C. With any luck, one of these two tricks will get the clutch to engage and them we can work on the finer points of the system actually cooling. BTW, when I bought my '83 300D, the connector had been pulled off the compressor. I plugged it back in, set the A/C to max and when the clutch kicked in, it STALLED the engine. And you know how hard that is to do on those torquey diesels. Compressor was completely seized up.
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Old 06-19-2003, 07:56 AM
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Okay, to begin with I think you need a new mechanic. I do not trust a mechanic that recommends replacing parts because "they've been setting up for a long time." I have had these compressors set up for years with no ill effect.

She is right, however, about buying a NEW R4 compressor rather than a rebuilt.

You need to start by turning the engine off and turning the front part of the compressor clutch by hand to see if the compressor is free. If it turns freely, then you have a good starting point. Since there was pressure on the system when you cracked open the shrader valve, you have a relatively tight system.

The second reason to find another mechanic is that anyone in the business should know that when you have a low charge, the low pressure switch breaks contact to the compressor. This is to save the compressor because if there is no refrigerant, oil does not circulate through the compressor.

With the engine off and ignition switch and a/c controls on, remove the two connectors at the pressure switch behind the right headlight assembly near the sight glass. Short them together and listen for the clutch clicking. If the clutch clicks, you need to charge the system. Since there is still pressure on the system, you should be okay with not evacuating, just charge it up.

Even though R12 is expensive, it will be MUCH LESS expensive to charge, than to start replacing parts, flushing and all the other things you must do for a proper conversion. Converting a system is almost always penny wise and pound foolish.

Good luck,
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Old 06-19-2003, 08:09 AM
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Geez Larry, that 100 words per minute paid off here.. while I was trying to word my post a little more gently, due to self imposed political views which encourage female mechanicing... I have to say that you are correct again .
Jassz, Please listen to Larry. You will be much better off.
And really consider buying the Mercedes Factory Shop manual on Air Conditioning and Climate control for your car... a wonderful procedure guide and money saver in the long and short run.
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Old 06-19-2003, 09:46 AM
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The only thing I would add to Greg's post is that a course in Quantum Physics will help greatly once you get the manual and have to deciphrr the steps in some jobs there.
Also a huge dose in patience as sometimes just finding the job on the CD can be a lot of work just in it's self.

I actually took the time to go through mine and log the pdf numbers for the jobs I knew I was looking at performing and then I copied them to a hard drive and renamed the things so that Icould actually figure out what they were about...
Took me several days of browsing but it has paid off in the long run.

BTW - Larry's advice is excellent as I just did this with my 1980 and as it turned out I was just low on R-12. it cost me 180.00 with R-12 and labor but the AC is cold and works with the orginal parts...
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  #6  
Old 06-19-2003, 10:10 AM
LarryBible
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Folks,

My comments regarding the mechanic had nothing to do with gender. They were based on what the mechanic said.

I don't care if a mechanic is male, female or what. If they can do the work and understand what they need to understand then I'm on board with them.

I would have said the same thing based on their responses.

Actually, my daughter would never be an auto tech, but she would make a great one. She understands things that I tell her and she is does amazingly well handling tools. When she started out at 16 with her 300D I made her do a brake job and a few other minor things. I was amazed at how she could do things like use a punch and hammer and other things even though she had never done ANYTHING like that before.

She knows a lot more about the inner workings of a car than most drivers regardless of their gender. In fact I think it causes problems because she knows more than the boys that she hangs out with.

My son on the other hand, never learned or cared much about cars. I would be afraid to drive a car on which he had just put the spare on the ground without checking the lug bolts first.

Gender doesn't have to be a factor in this.

Have a great day,
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Old 06-19-2003, 10:23 AM
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Larry, I was not implying your answer had anything to do with the sex of the mechanic.... I was saying that I was sitting here trying to figure out how to gently say exactly what you went ahead and said...
My wording was also not meant to imply that what BobK said was not correct...just that I heartily agree with the more severe conclusions which Larry expressed about the overall situation...
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  #8  
Old 06-19-2003, 10:51 AM
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I love this board... sigh...

Thanks for the suggestions of things to try. Will do that.

Fisherman, I have not been able to manipulate the CD manual at ALL. Meaning, I can't cut, paste, print, email, save... nothing. It seems to be 'read only'. It would be REALLY handy to print a page now and then and take it to the car!

As far as the mechanic.... finding one you REALLY like is difficult! Probably easier to find a mate! We had a mechanic that was great, but he quit doing that type of work due to health problems. Since then we have tried several but haven't been completely satisfied with any of them. Picking this mechanic had nothing to do with gender... I just called a place that specialized in diesels, they told me they had a Mercedes specialist, so that sounded good. I don't think I even found out she was female till the second visit, and it was a bit of a surprise. "Oh, you're a GIRL dragon!" (You have to have seen Shrek for that to make any sense). What I do like about her is that a) she is absolutely passionate about these older Mercedes diesels, and b) she is very chatty so we pick up lots of tips! She is actually off work now due to surgery, but we have asked if we can pay her for some technical advice only (not just the airconditioning).

LarryBible, if it doesn't work out with this mechanic, do you think your daughter could have a look??
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Old 06-19-2003, 10:57 AM
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Jassz, OK, I think I may have picked up on the problem... She is interested in the old Diesels.... you need someone interested in AIR CONDITIONERS....
I was suggesting you get the paper manuals... I have no clue how people deal with the CD's to work on their cars...

"finding one you REALLY like is difficult" UUUHHHHH Yes ... have you noticed a slight leaning towards talking people into DOING IT THEMSELVES here ? That is the root of that entire movement.
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Old 06-19-2003, 01:54 PM
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To address the original question, quantum physics is less complicated and is taught on many college campuses so the knowledge is widespread. On the other hand, there are precious few people who understand how a Mercedes air conditioner works, and I think most of them are members here.

Anyway, to add something useful to this thread, the auto parts store down the street sells R12 and I have several empty boxes at home that look sturdy enough to make it to Canada. Email me if you're interested. R12 gauges and can taps can be found on Fleabay. Does anybody know if its illegal to ship R12 across the border?
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  #11  
Old 06-19-2003, 02:07 PM
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leathermang,

I did not mean to imply that you were ragging me about the woman thing. I just didn't pick up on it and once you made mention, I realized that I'd best clarify or risk being drummed off the site by our beskirted mshop friends.

Have a great day,
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  #12  
Old 06-19-2003, 02:10 PM
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She might need her 609 cert for it to be legal for you to sell/send it to her...
But she needs that anyway......
She said R12 was not illegal up there....
I think all air conditioning parts should be confiscated from all Canadians and sent to Texas and Florida where they are really needed.
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  #13  
Old 06-19-2003, 02:13 PM
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"I don't care if a mechanic is male, female "--Larry Bible

Well I do ! I would like to find a cute single female mechanic...
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  #14  
Old 06-19-2003, 06:06 PM
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Good luck in your search leathermang Maybe she will have a job on the side as a lingerie model, and make a 6 figure income too.

Quote:
Even though R12 is expensive, it will be MUCH LESS expensive to charge, than to start replacing parts, flushing and all the other things you must do for a proper conversion. Converting a system is almost always penny wise and pound foolish.
Hmmm, I'm not sure that is true. I think their strategy is to make it AS expensive to recharge with R12 as to convert to the environmentally friendlier kind (I think it's R22?). I think R12 is priced at least 10X higher. I guess they figure you will be more likely to do the conversion if it costs you just as much to NOT do the conversion.

Which makes your offer very interesting Rick Miley. I will get back to you on that though, as my husband thinks they still have some R12 kicking around where he works that they can't use any more.
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Old 06-19-2003, 06:38 PM
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Jassz

Actually pdfs are pretty easy to deal with once you figure out where on the CD the job is that you actually want. They seem to regularly display a portion of a job in one selection and then in another they display the entire job, go figure...

When you find the one you want, write down the pdf number diplayed at the top fo teh screen. Then you can search the cd from your computers search function, right click the one you want and copy it, then paste it to a subdirectory on your hard drive and then chagne teh name to something a little more relevant than 01-356.pdf...

The only really negative thing about these cds is a lack of a search feature built into the CD. Man that would make the world go round for me...

Simple expectations in life I guess.

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