A/C leak check - change drier first?

[sigchuck]

Hi guys, I just finished some work on my AC system, including replacing condensers and evaporator. I did have to make one new hose, but this was due to a condenser change. The system was holding a charge great prior to me taking it apart.

I would like to leak check it prior to installing the new drier. Since the system was open to atmosphere for a couple weeks, do I need to vacuum down longer than the recommended 30 minutes just for a leak check? I do have a new drier in hand and plan to replace before charging, but don’t really want to install before I determine if/where leak is (I have quite a few fittings I would need to check, so just concerned about having new drier exposed to atmosphere for two long if there is a leak).

Thanks for the help!

[Peter M]

sig

Assuming you used new o-rings of the correct size, oiled them on installation and remembered to tighten each fitting - not too much and not too little - you would have to be very unlucky to have created a leak. Think positively! :-)

I would normally replace the drier last after doing any other work and draw it down for 30 minutes, check it holds a vacuum for another 15 minutes or so and then recharge with refrigerant then.

[sigchuck]

I tried vacuuming last night before changing drier. I would almost immediately get 30” on the gauges, but after 45 minutes when I’d close the gauges I would notice a slow leak. Tried again this morning and the leak is nearly immediately back to 0.

Probably a dumb question, but how tightly should quick disconnect fittings on gauges fit on the service ports? I ordered some new ones as mine are relatively loose. Hopefully this is the source of the leak!

[GH85Carrera]

Yes, absolutely change the receiver-dryer after you replace all the parts you need to replace.

Our 911s are not like other cars. 40+ feet of hoses, and components scattered from front to back. Water will turn to ice, and "hide" in the system and it can be a real challenge to purge all the moisture.

I use the "belt, suspender and glue" method of overkill to be sure all the moisture is eliminated.

Pull a vacuum for 3 hours or so. Let it sit overnight. Then I pressurize with dry nitrogen to 120 to 150 PSI, look everywhere for a leak with soapy water. 150 PIS will show a leak way faster then the -14 PSI of a vacuum. If no leaks are found, vacuum for three hours, purge one more time with nitrogen, then another three hour vacuum and hook up a micron gauge. Change to oil on your vacuum pump for that last 3 hour pull. Yea, that is an important step to have fresh oil in the vacuum pump for the final pull.

Your gauge set may show it at full vacuum, but a micron gauge will show you how much pressure there really is left.

If it has no leaks, charge with refrigerant.

There are hundreds of threads on AC on this site. Search for them, and grab a pot of coffee or beverage of your choice and sit and read. You will see how others have surmounted problems. A good vacuum on the 911 is a challenge. A 30 minute vacuum pull is not much more than a waste of time. 30 minutes may work for a front engine car with all the components within a few feet of each other.

You can never have too good of a vacuum, or too much money to spend on your 911.

[Tommy Z]

Glenn, You shared this same advice with me when talking about my charging issues. I know the Griffiths system is excellent and that my issues are all charge related so I went ahead and ordered a vacuum! Looking forward to it's arrival and following these steps as you've laid them out so I can finally get my system to perform the way I know it can. Thanks again!

[sigchuck]

Thanks, Glen - so to be clear, the "leak" that's presenting currently could be a function of the old drier being overly saturated with moisture or me not leaving the pump on long enough?

Maybe phrased another way, if I'm only trying to use the vacuum right now to establish whether I have a leak anywhere (which I understand isn't the best way to determine whether I have a leak), should it matter how long I let the pump run once I get it to 30"?

I would really like to avoid putting on the new drier until I'm ready to charge. If I do find a leak, three kids under the age of 5 tend to limit my ability to tackle a project in one sitting, i.e., finding the leak might turn into a 2 week process!

[88911coupe]

OK, have to throw my 2 cents in here...I just spent YEARS screwing around trying to get my AC performing after replacing pretty much everything. I knew I was not letting ambient air in during the recharge but it never worked very well UNTIL I finally took Glen and others advice to flush it with nitrogen a few times. Once I did that performance dramatically improved. Somehow no how many times I pulled a strong vacuum there was still "air" in the system. Keep in mind this was with every inch of hose being replaced. Hopefully you can get it to work without doing the nitrogen purge but if results are mediocre do NOT do what I did and wait. The nitrogen was about $150 out the door from any welding supply store, plus I had to buy a regulator. I'm still kicking myself for my stupidity.

[GH85Carrera]

The challenge with finding a leak with just a vacuum is you get a little over 14 PSI if you are at sea level. With a pressurization or purge of dry nitrogen you can run it up to 100 PSI, and see if that drops fairly quick.

In my experience, getting all the moisture out is a challenge in a 911 with all the hose, and components scattered everywhere from the front to the back.



Back in Jan of 2007, I was sick of the pitiful stock AC in our 911s. I coughed up the money for the full Griffith's 4 condenser solution. The ONLY parts of my system that are still OEM parts are the front and rear condensers. When I replaced my evaporator and all my hoses and added two more condensers, I hooked up the receiver/dryer last, and pulled a vacuum. My system had been open for the two weeks it took me to get everything back in place and hooked up. I would pull a vacuum, and the vacuum would not hold. I worked on every connection and was super careful to get everything clean, and the o-rings lubed with oil.

A friend of mine that was an AC pro told me about the nitrogen purge. He brought over his rig, and we only pressurized it once. Again I searched for leaks, and I was happy all was tight and leak free.

I pulled a 3 hour vacuum with fresh oil in the vacuum pump, and everything was fine for a trip through the desert to California in July and back home in total comfort.

Over the years I have had to replace the compressor, and I just bought the nitrogen rig from a local welding supply place. The nitrogen itself is 20 bucks or so and it would likely do 40 purges on the system, so it is cheap. I figure it can't get too dry or too good of a vacuum so I go nuts and do it twice. It is just time, and I figure a little more time up front will keep me from sweating, even in Key West in July.



The research I did on the internet showed how a bit of moisture in a vacuum with boil for a while, but then turn to ice, and just sit there for a long time. It was clear in a bell jar under vacuum that the ice just refused to sublimate. Getting all the moisture out is the challenge. So I go to my total overkill multiple stage nitrogen then vacuum. No pro you hire will do that for the price of the nitrogen bottle alone.

And the final step was find a micron gauge. I will admit, I am a tool junkie, and I prefer to have the equipment on hand to do it myself. I bought a micron gauge just to see how good is the vacuum. It showed me it is impossible to be accurate with just the AC gauges alone.

[Peter M]

Originally Posted by sigchuck

I tried vacuuming last night before changing drier. I would almost immediately get 30” on the gauges, but after 45 minutes when I’d close the gauges I would notice a slow leak. Tried again this morning and the leak is nearly immediately back to 0.

Probably a dumb question, but how tightly should quick disconnect fittings on gauges fit on the service ports? I ordered some new ones as mine are relatively loose. Hopefully this is the source of the leak!

sig,
Getting this right is important. Much more important than some of the other advice you have received so far.

Suggest you lubricate the o-rings in the fittings before you use them. They should be snug on the test ports but not tight. You should be able to try jiggling the fitting and not create a leak and immediately lose vacuum.

Hopefully your new vacuum fittings will correct this leak and you will be on your way and have confidence to replace the drier, draw a reliable vacuum and recharge with refrigerant.

[sigchuck]

Hi guys, I did lube all o-rings and was pretty confident in the crimping of the new hose I made. Good, but un-surprising news, is that the Harbor Freight gauges I bought several years ago have garbage service fittings. I went and borrowed a set from autozone this afternoon (probably only marginally better than HF, but wow the QD fittings on the HF gauges were junk), pulled vacuum for ten minutes, and the needles haven’t moved in three hours.

Assuming it holds overnight, I’ll swap in the new drier and attempt a charge after pulling vacuum again. Hopefully I won’t have any issues, but will definitely try the nitrogen if I can’t get a satisfactory charge.

[GH85Carrera]

At the very least, change the receiver dryer, pull a long vacuum, as in several hours of the pump running. And change the oil in the vacuum pump with fresh vacuum pump oil first. Let that sit overnight just to evaporate all the ice or moisture that will evaporate. Then run the pump another hour the next day before adding any refrigerant.

It is tempting to think a vacuum is a vacuum, but it just isn't. See if the tool places have a micron gauge to rent. You will see the vacuum get better and better with a long vacuum run. Or you should if the gauges and connections are not leaking.

Just a tiny amount of moisture can cause blockages at the expansion valve where the the refrigerant turns from liquid to gas and makes the cold you want. The pressures on the low side will be too high and you will not be happy.

[eastbay]

Another thing is most appliance parts houses carry a nice selection of AC gauges and hoses, along with hose service kits, which are the little gaskets and o-rings that go in the hose couplings.