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  #1  
Old 07-11-2007, 10:13 PM
Abandon the Roads!
 
Join Date: Feb 2007
Location: Texas
Posts: 283
And There Went the A/C

Well, my dad walked in after driving the Benz and notified me that it lost the A/C charge and that he wasn't sponsoring any further A/C repairs. Ho boy, here comes the Texas summer.
At some point I'll put a gauge on the low side while he's not there to check if it actually leaked it. Knowing him, he just observed that it wasn't blowing cold and figured it had leaked.
The trouble is that unless he set the ACC wrong (highly unlikely) the culprit is going to be $200+ (unless it's just a freon leak, but even then, I doubt it would get fixed). I do kinda see his point. After 2 compressors, two freon charges, the oil charges, the flushing, and oh so many trips to O'Reilly's, I suppose it's a lost cause.
Oh well, it ran for about a month, we go on a 2 week vacation, come back, and it's dead.

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1984 300DT turbo 138k mi

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  #2  
Old 07-11-2007, 10:17 PM
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Join Date: Oct 2005
Posts: 4,263
After two compressors, you don't have a gauge set? You really should check both sides.

And you could also take to a shop to have it checked for leaks. Maybe it's something easy.
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  #3  
Old 07-11-2007, 10:25 PM
Abandon the Roads!
 
Join Date: Feb 2007
Location: Texas
Posts: 283
We have a gauge set, two actually.

Well, my dad was not available to bother me, so I just went out and checked.
The car was hot but had been sitting at least 10 minutes, and I was getting 110PSI at the low side (car was off).
That's about right for a normal charge, IIRC.
lol, I'ma go check was the ACC was set on.
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1984 300DT turbo 138k mi

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  #4  
Old 07-11-2007, 10:30 PM
Abandon the Roads!
 
Join Date: Feb 2007
Location: Texas
Posts: 283
No such crazy luck there, the ACC was on normal.
I'm on summer break, so tomorrow I'll hook up the gauges again and do a full test. If it had a charge and wasn't blowing cold, the compressor is probably blown (I haven't had any electrical problems before).
It seems odd though, the compressor blowing after we were away for two weeks?
Unless the oil all drained into the compressor... can it do that?

I think this is my dad's insistence that flushing the condensor was enough coming back to haunt me.
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1984 300DT turbo 138k mi

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  #5  
Old 07-11-2007, 10:45 PM
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110 on the low side means that you certainly did not lose all of the charge. You need to ensure that the compressor is starting, and if so check the pressures. Until you know whether the compressor is running, you have no idea what's going on (but I don't think I'm telling you anything new).

The oil can't "drain" from the compressor. It's carried with the refrigerant.
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  #6  
Old 07-11-2007, 10:59 PM
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Your problem could be the evaparator temp regulator. It can "trip" at a much-too-high temperature, causing the compressor clutch to disengage. Typically, the a/c will work for a few minutes, then start blowing ambient air. This causes folks to think that the refrigerant charge has been lost.
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  #7  
Old 07-11-2007, 11:28 PM
Abandon the Roads!
 
Join Date: Feb 2007
Location: Texas
Posts: 283
Hokay, after a discussion, we did a full troubleshoot, and here are the results:
There is a slow leak somewhere (it was pulling down to about 25 PSI)
The aux fan seems to not be engaging when it should (need to find the conditions in which it should operate)

Also, there was an ominous clunking/rumbling sound, which had me really worried. Turns out the new compressor belt had stretched and was flapping. I'll have to get that tightened up, but it doesn't seem at all like it was slipping.
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1984 300DT turbo 138k mi

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  #8  
Old 07-11-2007, 11:47 PM
Abandon the Roads!
 
Join Date: Feb 2007
Location: Texas
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Okay, two things.
First, we're going to take out the kick panel and visible check for the leaks, degrease the hoses, and then put in some dye and maybe leak stop. Somehow, we're finding that leak.

Second, I'm mixing myself up as to the cycle the freon goes through. Pretty sure it's this:
compressor -(high pressure line)> exp valve -(low pressure)> evaporator ->exp valve ->dryer ->condensor ->compressor

So if I had low freon, the temp at the dryer would be lower and the fan wouldn't kick in.
I sat down with an A/C maintenance book and went through all this a while back, and it all made sense, but what's confuzzling me now is that when you look at the dryer sight glass, it should be clear, implying that the low pressure line is forming liquid because the pressure drops enough. Instead I'm getting a white fog which I assume is gas...
I think I mixed up here somewhere. Probably because it's 10:50 PM and the time zone change from the vacation is throwing my sleep off.
I like sleep, it makes me not feel tired.
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1984 300DT turbo 138k mi

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  #9  
Old 07-12-2007, 12:16 AM
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You're talking about finding leaks, but you as of yet haven't determined that you have one. Your "resting" low side pressure at what I'm sure was a temp in either the mid/high 80's or low 90's doesn't indicate to me a low freon condition at all.
As others have said, you need to put the gauges on (valves closed of course), turn on your AC, see if your compressor comes on, then watch your pressures and report back. Be sure and check it at around a 1500 rpm high idle.
Report back, and the smart guys will give you feed back. I'll be reading and watching....
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  #10  
Old 07-12-2007, 12:21 AM
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Quote:
Originally Posted by arew264 View Post
compressor -(high pressure line)> exp valve -(low pressure)> evaporator ->exp valve ->dryer ->condensor ->compressor
Not quite, but close.

Compressor outlet (high-pressure vapor) -> condensor input -> condensor output (high-pressure liquid) -> receiver (high-pressure liquid) -> expansion valve -> (low pressure liquid) evaporator inlet -> evaporator outlet (low pressure vapor) -> compressor inlet (low pressure vapor).
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  #11  
Old 07-12-2007, 12:44 AM
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Don't condemn the a/c system as being shot just yet. If you had a serious leak, it most likely wouldn't have held 110 psi while sitting untouched for two weeks. You need to make sure your compressor is coming on and cycling like it should. I'd imagine your summer days are a lot like mine so start it and set the a/c on max and after a few minutes your compressor will most likely stay on and your aux fan should kick on. You should at least see cooler than ambient temps. If it still feels warm, time to start checking things like whether or not the ccu is fully closing the monovalve, or possibly the monovalve itself. Check the compressor first to make sure its cycling properly.

If your belt was loose enough to be slapping around, it very well may have been slipping. It was posted somewhere on here that these compressors require somewhere in the neighborhood of 8hp and a loose belt can't transmit that. Don't condemn the compressor right away if you hear funny noises coming from it. Its not unheard of for the three 19mm mounting bolts to back out. Its happened to me and I've heard others talk about it.
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  #12  
Old 07-12-2007, 01:56 AM
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I don't know much, but ...

Some people just add freon. You need the oil in the freon to lube the stuff through your system, without it, the a/c ultimately won't work. Many people just add freon, and it ruins the compressor, etc.

jeff
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  #13  
Old 07-12-2007, 09:43 AM
Abandon the Roads!
 
Join Date: Feb 2007
Location: Texas
Posts: 283
I woke up this morning and realized I had misplaced the condensor and dryer in that cycle, so thanks, that makes the whole thing make a lot more sense (particularly the liquid/vapor part).

We did have gauges on it last night, and we believe there is a slow leak because we charged it in the evening (so the temperatures were very close), and we were testing it in the evening. That should make any difference in pressures due to temperature be fairly small.
When we charged it, the compressor was pulling the low side down to about 30 PSI, and when we tested it last night, it was pulling down to 25 PSI (20 PSI when we jumped the temperature switch to turn on the aux fan).

I'll take some high side pressures today, hopefully.


Good news is that my dad is back onboard since it seems to just be a leak.
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1984 300DT turbo 138k mi

Still hauling me to school and back.

Handy Site:
http://www.dieselgiant.com/
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  #14  
Old 07-12-2007, 09:48 AM
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Quote:
Originally Posted by sailor15015 View Post
You need to make sure your compressor is coming on and cycling like it should.

Check the compressor first to make sure its cycling properly.
Please tell us more about your compressor "cycling" theory.
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  #15  
Old 07-12-2007, 11:52 AM
Abandon the Roads!
 
Join Date: Feb 2007
Location: Texas
Posts: 283
I'm sure the compressor cycling is not the problem. Down here in Texas, the compressor doesn't "cycle" even if that's what the klima was designed to do. We're getting 90*F days already.
The clutch engages when you put the ACC in normal mode, and the compressor runs.

Also, yes, that belt probably wasn't transmitting the full force. I'll get it tightened up, but it still seems there's a decent sized leak to find somewhere.

So from here I need to get the belt tightened, degrease and visually check for leaks (though not in that order), and then use dye to find the leak if it isn't visible.
The aux fan... well, I think my dad has expectations for how it will work that MBZ just didn't follow. I read that it's supposed to turn on at 62*C at the receiver dryer, so basically it only works when the system has too much pressure or is operating very hot.
I have read about people putting in a relay so the fan turns on when the compressor is on, and it sounded like something good for me, as this car will be driven mostly to and from school at speeds of 35 MPH and lower.

Anyway, the leak checks come this evening and then the dye goes in. If all goes well, we won't need dye, but one way or another, we're tracking down that leak.
The problem is what to do when we find it.

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1984 300DT turbo 138k mi

Still hauling me to school and back.

Handy Site:
http://www.dieselgiant.com/
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