Nitrogen vs Argon/CO2 mix to pressure test an AC system?

A930Rocket · 06-03-2011, 02:37 PM

Tomorrow I'm going to replace the receiver dryer and evecuate the AC system on my BMW.

Since I don't have a nitrogen bottle to pressure test my AC system on the BMW, can I use my welding argon/co2 mix?

MarKoBrow · 06-03-2011, 02:48 PM

No it will contaminate the system, you should be testing via a vacuum pump and gauges to check for leaks or a dye that gets added with the 134A

lm6y · 06-03-2011, 03:49 PM

Not sure about the Argon / Co2 mix, but nitrogen is perfectly fine to use. Nitrogen has no moisture, so it won't contaminate the system. Many A/C shops use this method. But whichever you do use, vacuum it down, and check that way too. I've seen leaks not show up under pressure, but will leak under vacuum.

A930Rocket · 06-03-2011, 04:38 PM

Yes, I'm going to pump/evacuate it with gauges before hand.

I was just thinking that a pressure test with maybe some soapy water might be an option to find leaks. They guys do it on the homes to determine if it leaks.

Especially with the coolant/freon costing so much.

Tim Hancock · 05:12 PM

Quote:

Originally Posted by A930Rocket

Yes, I'm going to pump/evacuate it with gauges before hand.

I was just thinking that a pressure test with maybe some soapy water might be an option to find leaks. They guys do it on the homes to determine if it leaks.

Especially with the coolant/freon costing so much.

I just pressurized my 911SC yesterday to find a slow leak.

I got my old stock AC working and switched to 134 about 4-5 years ago on my SC by pressurizing the system with air and then spraying everything with soapy water (I simply dump about an ounce of dish soap in a spray bottle filled wih water) to find the leak (AC line by the jack port was damaged by the PO and was the source of the leak). I fixed the leaking hose, then installed a new drier then evacuated the system with a vacuum pump prior to charging with some oil and 134. It has worked great for the past several years needing only a can of 134 each spring. This spring it no longer worked and after hooking my gages up it read only 10psi prior to running so I knew I had a leak to fix again. Isprayed everything down and found no visible bubbling leaks so I reluctantly pressurized with compressed air to about 40psi..... still no visible leaks..... I pressurized to 70 psi and resprayed eveything and low and behold my 4-5 year old drier had a leak that showed up by bubbling the soapy water solution.

I just bought a new drier and after installing, I will put the vacuum pump on it for a couple hours then recharge with 134 just like I did 4-5 years ago and all will be well again.

While pressuring with air seems like bad idea, if you have a system that completely leaked out, it will have been exposed to air anyhow. So long as you vacuum the system for a long time to boil off the moisture, it will be fine. I am fairly confident I would not have found this latest leak using only the -14 psi that a vacuum produces.

A930Rocket · 06-03-2011, 06:33 PM

Mine is working, just not very well. I added some 134, but who knows what was in there before hand. I want to empty it, replace the receiver dryer and use some more 134. I may do as you did and see what I find before opening it up.

I've seen where guys pressurize them to 200 psi. Seems like a lot to me.

Quote:

Originally Posted by Tim Hancock

I just pressurized my 911SC yesterday to find a slow leak.

I got my old stock AC working and switched to 134 about 4-5 years ago on my SC by pressurizing the system with air and then spraying everything with soapy water (I simply dump about an ounce of dish soap in a spray bottle filled wih water) to find the leak (AC line by the jack port was damaged by the PO and was the source of the leak). I fixed the leaking hose, then installed a new drier then evacuated the system with a vacuum pump prior to charging with some oil and 134. It has worked great for the past several years needing only a can of 134 each spring. This spring it no longer worked and after hooking my gages up it read only 10psi prior to running so I knew I had a leak to fix again. Isprayed everything down and found no visible bubbling leaks so I reluctantly pressurized with compressed air to about 40psi..... still no visible leaks..... I pressurized to 70 psi and resprayed eveything and low and behold my 4-5 year old drier had a leak that showed up by bubbling the soapy water solution.

I just bought a new drier and after installing, I will put the vacuum pump on it for a couple hours then recharge with 134 just like I did 4-5 years ago and all will be well again.

While pressuring with air seems like bad idea, if you have a system that completely leaked out, it will have been exposed to air anyhow. So long as you vacuum the system for a long time to boil off the moisture, it will be fine. I am fairly confident I would not have found this latest leak using only the -14 psi that a vacuum produces.

MarKoBrow · 06-04-2011, 01:02 AM

Quote:

Originally Posted by A930Rocket

Mine is working, just not very well. I added some 134, but who knows what was in there before hand. I want to empty it, replace the receiver dryer and use some more 134. I may do as you did and see what I find before opening it up.

I've seen where guys pressurize them to 200 psi. Seems like a lot to me.

Perhaps you might want to check your pressures before recharging, it sounds more like you have a expansion valve that is getting clogged

billybek · billybek's Garage

Quote:

Originally Posted by MarKoBrow

Perhaps you might want to check your pressures before recharging, it sounds more like you have a expansion valve that is getting clogged

This is a very good possibility if R-134a was added to a system that had mineral oil in as a lubricant.
You can leak check a very small system with a standing vacuum test. You should let it stand for 24 hours blanked off from the pump. A big leak will show up fast, a very small leak won't.
If you have removed the refrigerant to do a repair and need to do a leak check (good idea) there will probably be enough refrigerant left in the system and in the oil to work as a trace gas when the system is pressurized with dry nitrogen. Then you can use an electronic leak detector that is capable of finding very small leaks.
You could do a standing pressure test, but changes in ambient temperature may give you the impression that the pressure has changed.
If there is a question as to what refrigerant you have in the system, if there is enough refrigerant in the system to exist as both liquid and vapour, you can check the saturation chart to determine what refrigerant you have in the system. If you have a blend of refrigerants installed (ex R12 replacement gas and R12) you will not be able to determine what gas is in the system this way.
A vacuum gauge is a valuable tool when evacuating a system. You can test the ability of the pump to pull a good vacuum. (some can't) and the vacuum level inside the system. Even if you have the smallest of leaks, you will not be able to reach below 1000 microns. A good vacuum is 500 microns, acceptable is 750 on an system with residual oil/refrigerant.
Don't forget to do regular oil changes on the vacuum pump. Old oil with moisture in it will reduce the ability of the pump to pull low.

mattdavis11 · 07:01 AM

If you understand the boiling point of moisture while under vacuum, use compressed air. If not, try other methods. Use common sense though, if you have a stream of moisture coming out of your air nozzle, move on to another method or set up an inline filter/drain the tank and line.

Never had a problem using compressed air, and do use nitrogen occasionally to test for shaft seal leaks while submerging the compressor in water.

I've seen systems that leak under pressure but don't under vacuum. When you suck it down, the o-rings contract sealing it up, but when you pressurize the system, they return to a state where they leak.

100PSI will find your leak just fine.

A930Rocket · 11:57 AM

I put the gauges on the car and the pressures were low. Low side was ~10 and the high side was ~130.

I vented the freon into a bucket [

] and hardly any came out.

Swapped out the receiver dryer and I now have a Robinair pump on it.

I'll see if it holds a vacuum and either pressure test it or do a fill and see how it does. I'll need some adapters to get my
compressor to work.

BTW. Is the schreader valve the sane as a wheel? I my want replace one as it seems a little off

Tim Hancock · 06-04-2011, 11:47 AM

Quote:

Originally Posted by A930Rocket

Mine is working, just not very well. I added some 134, but who knows what was in there before hand. I want to empty it, replace the receiver dryer and use some more 134. I may do as you did and see what I find before opening it up.

I've seen where guys pressurize them to 200 psi. Seems like a lot to me.

If you have a leak, I think you will find it with soapy water if you just use up to 100 psi. I have done this leak finding technique with several of my old P'cars and have found compressor leaks, drier leaks and hose leaks which once fixed all resulted in a successful charge with 134.

I switched my '92 BMW 325i over to 134 after finding an o-ring leak at the expansion valve (just added a new drier, an oil charge/134 mix and 134..... hoses and seals remain stock). I did this when I first bought the car used in '98 with 140k on the clock. It now serves as my daily beater/driver with 320,000 miles and the AC still works great with only needing a can of 134 every 3-4 years to top it off. Your '91 might have different components as that was around the time frame that 134 was coming on the scene. My '92 originallycame with r12, but I think it had 134 compatible components. All my older Porsches still have their old r12 hoses and they do not leak much if at all as they had soaked for years in mineral oil which pretty much seals them up effectively in old cars. IOW, brand new r12 hoses leak 134..... old r12 hoses generally hold 134 fine in my experience with several switch overs I have done on my cars.

A930Rocket · 06:34 PM

Got a conversion kit for 134, but I can't close the hood because both fittings hit the hood or hood hinge. In addition only one fitting fits and I'll use it on the low side to add the 134, but I need a 90* elbow to close the hood.

Going to a movie, so I'll have to go to the main parts store tomorrow to get the needed parts.

EDIT: just checked and it's holding a vacuum 3 hours later.

mattdavis11 · 04:37 AM

There are different size R12 fittings, I forget which they are, but I believe the low side is a 5/16 and the high is 7/16ths. Remove the old valve cores as the new fittings will obviously have them.

I left my high side R12 just in the event that if it does visit a shop or lube place, it would cause some consternation for some high school drop out that may want to jack with my system. It's doubtful that they would even know where the low side is, so it's 134. I have to use both sets of gauges, but that's alright.

If you want, you can leave both R12 and get a can tap that punctures the side of the can. They have adjustable taps that can pierce any size can. I wouldn't advise many people to do this, but you have a 1991 318, which are highly sought after, and leads me to think that you aren't going to pass it along.

Tim Hancock · 05:25 AM

I also use my old r12 gage set on my 911 but I run 134 in it through the stock York valves ..... I have a bunch of adapter fittings I acquired/made over the years for hooking up cans/vacuum pump/hoses/etc to my gage set and my various cars..... does not matter to me what fittings my cars have. My cars will never go to a shop for AC service so there is no worries about a shop contaminating there systems although I do have stickers in the engine compartment to signify that I have 134 in the system.

mattdavis11 · 06-05-2011, 06:21 AM

I'm kind of richard head when it comes to a/c, I don't put stickers on my cars. If I had to leave any of my cars, for say an inspection or alignment, and they contaminated their stuff by jacking with my system, they deserve it.

More than likely, I'm taking my car to a shop I sell a/c parts to, and hopefully we won't have to sit down to have a chat. We send out "tattle tails" with a/c kits to keep warranties down. They're essentially tie wraps with caps that go over the service ports. Too many people are eager to hook up to the a/c system these days.

EarlyPorsche · 06-05-2011, 06:22 AM

Reading all these posts make me dread going out to the driveway to replace AC o-rings in my truck before taking it to someone to vacuum and charge.

mattdavis11 · 06:41 AM

Tell them to suck it down, then go buy some cans at Wally world. It prevents you from seeing the pressures if you don't have guages, but you know there are no contaminates in the system. Ideally, you want to do the work yourself.

Figuring out how and why you have to replace certain components is not something I can teach through a keyboard. However, you said truck, how's the fan clutch? Is it a Dodge?

lm6y · 06:39 AM

Now guys, federal law REQUIRES you to have the correct fittings, a sticker describing when, and where the retrofit was done, AND a high side cutoff switch to keep from blowing anything, and venting refrigerant into the atmosphere.

Has anyone EVER done it the "legal" way?

mattdavis11 · 07:10 AM

I do it the legal way when it's proscribed under law. I can do whatever I want with my own stuff.

A930Rocket · 06-05-2011, 01:17 PM

Pumped it back down again for an hour, then held vacuum for an hour.

I used Freeze 12 to charge it with my R12 gauges and a side can dispenser. Low side was 76 PSI and the high side was 225 PSI.

I'm getting 50-60* out of the center vents on a 85* sunny day. I was hoping for colder, but I'll see if it lasts and go from here. Any ideas on making it colder?

One thing I had to do was add a drop of solder to the tip of the schrader valve. I replaced it with a new one, but it was still just low enough the hose fittings wouldn't push it down to pump or charge.

Holding vacuum for an hour

Low sides

High side