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  #1  
Old 01-27-2010, 10:06 PM
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what are the weak links in an auto AC system?

If an AC compressor ran continuously (e.g., no evaporator temp sensor to prevent icing) then the system lost pressure, what are the likely leak points?

Thanks,
Sixto
87 300D
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  #2  
Old 01-27-2010, 10:32 PM
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O-rings? Have you tried to pressurize the system WITH some AC dye and scan with a blacklight?
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  #3  
Old 01-27-2010, 10:35 PM
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if it did that than it has blown out the reed type valves in the high pressure side or maybe both and the compressor has gone away - jz
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  #4  
Old 01-27-2010, 11:36 PM
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The weakest link in most automotive AC systems is the evaporator- the heat exchanger that cools the inside air.
It is the weak link for many reasons

1) Its a heat exchanger - lots of connections and pipe joints, thermal stresses.
2) Its crammed into a small space, near the always-hot heater core
3) if it gets dirty, it will get clogged and freeze up, the ice formation inhibits cooling and further temperature-stresses the metal
4) its in the most difficult/expensive place to find and replace =)
5) Its also in the toughest place to diagnose (in order to see dye leaking out, you have to look into the vents or the drain line....


In my limited shadtree mechanic experience, 7 times out of 10, if there is an AC leak, its from the evaporator. Inject UV dye and look down the vents (each one) around the drain line, run the system a lot to disperse the dye.

I've also seen leaks around the compressor shaft - the UV dye will show up between the A/C clutch pulley and the compressor housing.

you need to get that dye in the system if you want to know for sure

-John
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  #5  
Old 01-28-2010, 11:16 AM
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I am pretty sure the AC compressor on my 19 year old 560 SEC simply has, just totally, seized up.

It threw its belt, so that when it let go, it whipped around the one for the alternator and tore that one to pieces, too.

Replaced both belts and it did the same thing again 2 days later.

So...


The car is now running on the alternator belt only, and the HVAC one is off, for the winter, don't need AC for this snowy weather, and you can now see where the now bare AC pulley has rubber all over it from where the belt could not move and fused itself to the pulley.

I will be waiting to warmer weather to buy a new HVAC conpressor and another belt to try and take care of it.
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  #6  
Old 01-28-2010, 11:24 AM
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A refrigerant sniffer works best for indentifying a leaking evaporator. Any shop doing A/C work will have one.
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  #7  
Old 01-28-2010, 11:24 AM
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Sorry to hear about that, Jim!
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  #8  
Old 01-28-2010, 12:01 PM
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Quote:
Originally Posted by Chas H View Post
A refrigerant sniffer works best for indentifying a leaking evaporator. Any shop doing A/C work will have one.
Got to be careful though. Some of those sniffers are tricky. A good trick they do is make sure the sensor accidentally hits something and it will go off so they can say "See!! There is one leak"
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Old 01-28-2010, 12:58 PM
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Quote:
Originally Posted by aklim View Post
Got to be careful though. Some of those sniffers are tricky. A good trick they do is make sure the sensor accidentally hits something and it will go off so they can say "See!! There is one leak"
There's no other way to identify a leaking evaporator in many cars. I used one to pin down a leak in my E320. Being carefull is part of everyday life.
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  #10  
Old 01-28-2010, 01:10 PM
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I use a sniffer in conjunction with UV dye. I just replaced the evaporator in my Miata this past week due to a pinhole leak. Sniffer picked something up, but UV dye confirmed it. After replacing the evap, I found a leak (using UV) at the high-side o-ring on the compressor. It evidently blew out when the TXV stuck closed (long story). Anyway, after replacing TXV, drier, evap, and some O-rings, I finally have A/C back in the car. I'm glad I chose the winter to work on it!
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  #11  
Old 01-28-2010, 01:17 PM
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You can typicaly find a sniffer at a pawn shop. Take a can of R-134 along with a tapping hose so you can release a bit of 134 and test it. I have found tiny leaks with mind, so I no longer use the dye. But then, it is a personal preference depending on which one works the best for you.

If you compressor seems locked-up it just might be the compressor clutch. BEWARE--- If your compressor clutch is frozen up then just replacing it will likely cure the trouble for only a few weeks. When the clutch is worn out the compressor is just about shot as well.
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  #12  
Old 01-28-2010, 01:26 PM
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The compressor engages and doesn't make untoward sounds when the low pressure switch is bridged.

Can a shop find leaks in an R12 system without filling with R12?

It's not a slow or gradual leak. The system worked one day, didn't work the next. Zero pressure on the high and low sides with the compressor disengaged.

Sixto
87 300D
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  #13  
Old 01-28-2010, 03:18 PM
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Quote:
Originally Posted by sixto View Post
The compressor engages and doesn't make untoward sounds when the low pressure switch is bridged.

Can a shop find leaks in an R12 system without filling with R12?

It's not a slow or gradual leak. The system worked one day, didn't work the next. Zero pressure on the high and low sides with the compressor disengaged.

Sixto
87 300D

they can fill it find the leak and unfill it charging you for the lost R 12 its the way we did it - jz
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  #14  
Old 01-28-2010, 03:26 PM
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No need to waste precious R12. Just put a $8 can of R134A with UV dye into the system yourself. Turn the A/C on for about 1 minute to circulate, then shut it off and go searching with your black light. The R134A eventually evaporates out of the system, and there's no harm done.
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  #15  
Old 01-28-2010, 03:29 PM
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Quote:
Originally Posted by gmercoleza View Post
No need to waste precious R12. Just put a $8 can of R134A with UV dye into the system yourself. Turn the A/C on for about 1 minute to circulate, then shut it off and go searching with your black light. The R134A eventually evaporates out of the system, and there's no harm done.
I used to see them but not anymore. Not even sure if you can buy it without a license. I wouldn't put R134A into the system if the oil and the O-rings are not built to take it. Isn't the oil different? Besides R134A isn't the same stuff as R12 and it doesn't cool as well and certainly not in cars that are not designed for it.
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