System not holding vacuum

[jorge]

Hi everyone, I'm going nuts with a VW Golf Mk7 that a customer bring to us to fix and recharge the AC system.
Recovered about 100g, after that tried to vacuum the system and the problem started to appear, my vacuum gauge was not going bellow 8000micron after about 30min of vacuum. After disconnecting the vacuum pump it rises to about 75000micron in a few minutes and stays there.

Tested the system with 15bar(~200psi) of nitrogen for 24hour and for my surprise it kept the pressure steady.

Something is giving in vacuum but not in pressure.

Is there a procedure to find out without starting the disassemble the system?

[dannyual320]

jorge, I've been wondering about the same thing. I'm sure one of the ac gurus on this site will come in to comment soon.

Here is a link to my other car forum, (Deleted). If you click on it, scroll down to post #12 and read what Gene wrote in his third paragraph.

(Deleted)

If you don't want to click on it, here is what he wrote:

And to let people know something I never see anyone talk about... a used compressor shaft seal will never hold a good vacuum, but it will hold pressure. A new seal or new compressor will hold vacuum.

Gene is an auto ac tech and he seems to know his stuff so if he says something like this, it's probably worth at least looking into it.

[JohnHere]

Recovered about 100g, after that tried to vacuum the system and the problem started to appear, my vacuum gauge was not going bellow 8000micron after about 30min of vacuum. After disconnecting the vacuum pump it rises to about 75000micron in a few minutes and stays there.

Chances are, it's the compressor shaft seal as previously mentioned, although the vacuum leak could be anywhere. Can you rig up some fittings that will allow you to pull a vacuum only on the compressor? If not, you could try replacing the seal. But your best bet is to replace the entire compressor—always with a new unit—not a rebuilt, along with the R/D. Of course, you'll be gambling that the vacuum leak isn't someplace else.

Also, I suggest flushing the rest of the system (and possibly replacing the condenser) since the vacuum leak introduced air and moisture into the system.

What year is this vehicle, and how many miles (kilometers) does it have on it?

[jorge]

Hello, thank you both for you help.

The car is a VW Golf Mk7 year 2014 with around 100k miles.


Now I'm almost sure that the problem is the shaft seal. I tested again for some hours with 20bar pressure, again no measurable loss. After that I released the pressure and tried to vacuum, this time it started to behave fine and going down, waited a few minutes until it started to stabilize around 2000micron. Then I started the engine a few seconds to move the compressor shaft since it's a clutch less compressor. Right after that the micron gauge started to rise fast to 20000 micron or so and the vacuum pump started to letting fog out of the exhaust . Left it like that for 2 or 3 minutes to see if the rise was caused from the oil agitation inside the compressor or a leak, the vacuum never dropped again so it was a leak...

What do you guys think about this?

[tbirdtbird]

"Can you rig up some fittings that will allow you to pull a vacuum only on the compressor?"
This is still a good idea.
And BTW you typically cannot get more than 100K out of a compressor

[tbirdtbird]

There is no hard and fast rule about shaft seals and o-rings leaking under vacuum or pressure. It can go either way. A successful vac test doesn't necessarily mean it will hold pressure and vice versa.

A comp with 100K is a tired comp by any definition.

[jorge]

I don't have fittings to test the compressor alone. We have some "universal" fittings for flushing but I don't think they will hold the vacuum.
Anyway right now we will have to ask for customer permission to proceed, this was supposed to be a simple leak test and re-gas.

On compressor mileage I don't know, I have seen much compressors with double or more miles without issues. My own car is on the original Sanden one with almost 600k km, only had to change the pulley bearing and hub once.

[JohnHere]

I don't have fittings to test the compressor alone. We have some "universal" fittings for flushing but I don't think they will hold the vacuum. Anyway right now we will have to ask for customer permission to proceed, this was supposed to be a simple leak test and re-gas. On compressor mileage I don't know, I have seen much compressors with double or more miles without issues. My own car is on the original Sanden one with almost 600k km, only had to change the pulley bearing and hub once.

Repairs on MVAC done correctly usually don't turn out to be simple and inexpensive. All depends on how much money the owner is willing to put into it. If the vehicle is in good shape and he/she doesn't want to buy a replacement car, the expense of repairing the A/C the right way might be well worth it. Please let us know what the owner decides to do.

[jorge]

Sometimes it's only a valve core or new o-rings...

The customer refused to go further for now.

[JohnHere]

Sometimes it's only a valve core or new o-rings...
The customer refused to go further for now.

As we know, sometimes the fix is simple and oftentimes not. I wish people would spend the money and get the leaks repaired for the same reasons you so eloquently explained earlier, instead of recharging the system every time warm weather arrives.