Help to ck AC for leaks - Atlanta?? - Page 9 - PeachParts Mercedes-Benz Forum

funola · #**121** 09-07-2016, 10:24 AM

Quote:

Originally Posted by tyl604

OK - back to the original purpose of this thread:

Is there anyone in Atlanta who has nitrogen and can help me pressurize my AC system to look for leaks?

Thx

What will you do next if you found someone that can help you and finds a leak (a certainty)?

funola · #**122** 09-07-2016, 10:32 AM

Quote:

Originally Posted by lorainfurniture

Maybe they leak when under positive pressure and not in vacuum? Maybe that front seal isn't supposed to leak at all?

Truth is, I really don't know. All I do know is that I pumped the system down to less that 500 microns, and the system stabilized somewhere slightly higher than 500. It held for at least 30 minutes. If I would have saw the gauge continue to climb, I would have assumed I still had a leak. I was unaware of the "intentional leak" that you mention

I recall speaking to an engineer at Compressor Works a few years ago and was told the ceramic front shaft seals of old GM R4's has a built in leak. The industry has stopped using ceramic seals at some point (in the mid 80's early nineties ...not certain of the dates). The new seals are double lip teflon seals and has a much lower leak rate than the old ceramic seals. Were you talking about an R4 compressor and do you know what type of seal it has?

leathermang · #**123** 09-07-2016, 10:32 AM

Quote:

Originally Posted by lorainfurniture

I didn't keep my stopwatch handy when I pulled the vacuum. I must admit, "several hours" was probably an exaggerated response.

It was at least 30 minutes, but probably not longer than 1.5 hours.

Do you even use a micron gauge?

Thanks for ceding the ' several hours ' to ' at least 30 minutes' as an exaggeration... so understandable in the heat of posting excitement.
BUT the difference in the two hardly requires a stopwatch to determine...

I do not own a micron gauge.

ALSO... you will never see any of my recommendations over the years suggest that anyone needs one to do a good job following industry standard AC fixes on automobiles...

It APPEARS that you are using vacuum to check for LEAKS in the system.. even after admitting that the seals may perform differently under vacuum than under pressure.
Correct me if I got the wrong impression on that.

VsTech and I have for a long time recommended pressure as the proper way... since that is the working condition... to check for leaks... it also provides a ONE STEP leak locating procedure inherent in its application..

where using a vacuum may be pulling the seals into a sealing position and if there are leaks does not provide any ( preferably sniffing ) pointing to the exact site of the leak.

So the need for a micron gauge is eliminated by our recommended processes and order of procedures.

Use a dry gas with a sniffable EPA ventable additive (R22?) to find any leaks.
Vacuum to remove as much moisture as possible.
Use new oil in the vacuum pump.
Use new oil added to the flushed AC system.
Add a new receiver dryer at the very last moment kept capped until then.
Use dry gas pressurized and evacuated three times to check for leaks at the connection points of the receiver dryer.
Use proper color Nylog to attach all the connections in the AC system.
vacuum the system and then insert the refrigerant.

lorainfurniture · #**124** 09-07-2016, 04:51 PM

Leathermag:

I do not use the micron gauge exclusively for leak testing. My process is as follows:

1. Pressurize system to 180 psi with nitrogen
2. Bubble test
3. If bubble tests pass, I leave the car pressurized overnight.
4. If car holds 180 psi +- 3 psi, I say the system is tight.
4a. replace filter dryer
5. pump down for 15 mins
6. refill with nitrogen
7. repeat 2 more times
8. Vacuum for about 30ish minutes, until I read under 500 microns
9. wait for 30 ish minutes to ensure the gauge does not rise ( this indicates a leak)
10. if no leaks, I disconnect all hoses except the low side port
11. Charge the exact weight of refrigerant
12. enjoy 40 degree vent temps in 90+ degree ambients.

The micron gauge is a valuable tool. It can detect a leak that bubbles or a sniffer just cant find. It wont tell you where it is, just that you have one.

Just for the record: I have done this successfully to 2 different MB's, an 89 300e (r12), and more recently my 93 300te wagon (r134). My proffession is appliance repair, so most of my knowledge is in changing dryers and compressors on residential refrigerators. The basic concept is the same, just household appliances MUST be tight as they only hold 4 ish oz. of refrigerant. Even the smallest leak will cause the fridge to go bad again in just a few short months.

I never had any formal schooling, My first attempts on refrigeration was on my first old benz, with the help of this forum. from there, I read a few books, bought some tools, and learned by just doing it.

tyl604 · #**125** 09-07-2016, 07:41 PM

Fun - will cross that bridge when I come to it. Wonder if Pelican sells a complete set of orings for it?

Found it - in July 2011 Joe from Lawrenceville helped me shoot in some Freon. His handle is Ether but I do not know if he is still around. Will try sending him a PM.

leathermang · #**126** 09-07-2016, 09:11 PM

Quote:

Originally Posted by funola

..... lower leak rate ......

The important point is that either of them do leak some.. so this is where using R12 or R134a INSTEAD of a blend... becomes cheaper and easier ( aside from how hard it is to find anyone to service any other refrigerants )...
If a system has a blend then when some of the refrigerant has leaked out...... then one can simply add a few oz to replace that gone..
But if the system has a blend... ALL of it has to be evacuated to bring it back to proper fill because the smaller molecules will leak out first... so your blend ratio is messed up...