jd 4450 ac leak can not find

HI
My system was the old r12 system and needed compressor and lines, so I have updated it to the r134 kit, new compressor, all new lines, new quick couplers under the cab, condenser and evaporator changed as well, plus all new o rings, I'm dry nitrogen testing the system and have a leak and cannot find it, I have a squirt bottle with soap and water mixed in and have sprayed all the connections and no signs of a leak, I have rechecked all my connections and the o rings and everything looks good, anyone have any ideas?
Thanks

On cars we would put a florescent dye in the compressor oil and then use a blacklight to see where it leaked. Might be worth a shot in case it's somewhere you aren't able to see very well. I need to do this to our 4630 soon, AC was converted a few years back. Didn't wanna blow cold this year so I just added a can, but it didn't last.

You will need a good quality refrigerant leak detector. Either way if you change from R-12 to R134-A you're going to have to check for leaks. Fifty series used R-12. If you switch to R-134 the performance will be compromised at best. Everything must be perfect when switching to 134: Change oil, filter/dryer, flush system, etc. If after all of that and it worked the day you charged it and it doesn't work a week later then you have a refrigerant leak.

I don't know what a "dry nitrogen test" is? Do you mean you are pressurizing the system?

I have all sorts of equipment for detecting AC leaks and sometimes none of them work.

I often find the one thing that often finds the problem when other more common tests do not? Hook an air-chuck to a charge-port. Pressurize to 150 lbs. and then just go over everything with a spray bottom of soap-water and look for bubbles.

What happens when you put a vacuum on it? Does it hold full vacuum for day with no loss?

I find that with some problem AC systems, no vacuum leak shows and not pressure leak shows when the system is working. But once you turn off the engine and let the low-side pressurize - sometimes that leak will show with dye but that is only at around 60 PSI. Thus why my test with 150 PSI from my air-compressor often finds the problem when other tests do not.

One other comment. When 134A first came into use, it was believed that the rubber AC hoses made for R12 would leak with the smaller molecules in the 134A. So since then, all new rubber hoses are "barrier" hoses with a special lining inside. Not sure if you have new hoses made for 134A or not. Now adays all new AC hose is "barrier" hose so the descriptive word is often not even used anymore.

(quoted from post at 14:57:21 09/20/19) HI
My system was the old r12 system and needed compressor and lines, so I have updated it to the r134 kit, new compressor, all new lines, new quick couplers under the cab, condenser and evaporator changed as well, plus all new o rings, I'm dry nitrogen testing the system and have a leak and cannot find it, I have a squirt bottle with soap and water mixed in and have sprayed all the connections and no signs of a leak, I have rechecked all my connections and the o rings and everything looks good, anyone have any ideas?
Thanks

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WOW, you sure did this job "right"!

ASSUMING there's no defective new parts and you didn't mangle any O-rings when you made the connections, there's not many places it could be leaking.

Wonder if it could be at the compressor shaft seal, either defective/damaged, or simply needs to be run to circulate some oil to it and "break it in" a little?

That being said, I find it amusing to read some of the responses, including a couple from the "smarter than most" (at least in their own mind) that don't know what it means to purge and then pressurize a refrigeration system with dry nitrogen!

Sounds to me like you did a thorough job. At this point about all you can do is pull a vacuum, add some dye, oil and refrigerant and run it till the faulty component show's up. Hopefully it's just a dry seal that will fix itself.

BTW, for those who don't know the dry nitrogen is used to pressurize the system without adding the moisture an air line will introduce.

sometimes I pressure with propane

Did you replace the steel lines in the rear cab post?

(quoted from post at 07:51:41 09/21/19) Did you replace the steel lines in the rear cab post?

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Ditto

I had a leak this summer in a line right where the tube with the nut goes in to the crimped end on the hose. Just an occasional little bubble would pop out of it.

I cannot imagine how common air introduced into the system via a shop air-compressor can harm anything. When done testing, a vacuum properly put on the system will boil out any trapped moisture.

I have been testing problem AC systems with compressed air for many years and cannot say I ever had a problem with it. Not even a bad receiver/drier.

I have got really fed up sometimes leak testing and have unbolted the compressor, with lines attached and immersed it in a bucket of water to check for leaks. Extreme? Maybe, but it eliminated a possibility really quick.
Nice thing with checking with Nitrogen is the ability to test at pressures similar to actual operating values

Ahh, there you are !

"I cannot imagine how common air introduced into the system via a shop air-compressor can harm anything. When done testing, a vacuum properly put on the system will boil out any trapped moisture."

I have spent the last 38 years as a commercial/industrial HVAC tech, so I have a bit of experience with the issue. There is no way I would ever pressurize a refrigeration system with shop compressed air. Not only are you introducing moisture into the system but oils and other contaminants as well. That is still going to happen even if you have an air drier and coalescing filters as they simply do not clean the air to the standards required for refrigeration systems. Moisture in refrigeration systems is measured in PPM and if you shoot even a small slug of condensed air line moisture into the system, you are going to spend a lot of time with your vacuum pump. You see, it doesn't take a lot of moisture pulled out of a system to destroy the pumping capability of vacuum pump oil and drying out a system in such an instance will take a number of oil changes. But even when you do get it dehydrated properly, you still will have introduced traces of air compressor oil into the system which has waxes and other components that do not play well with refrigerants and will lead to premature failures in the system. No professional worth his salt would ever deliberately introduce contaminants into a refrigeration system.

As for the leak, it was not mentioned how fast the dry nitrogen charge leaked down, so that makes giving correct advice somewhat harder. Checking for a fast leak with soapy fluid is hard because the leak will often blow the fluid away before a bubble can form. You can add florescent dye, as mentioned, but that is a avenue of last resort. My advice is get a good leak detector and mix a little 134-A in with the dry nitrogen and go over the system first. I would also try front seating the compressor service valves to isolate the compressor, then pressurize that to check the shaft seals.

Hello thanks for all your posts, yes all lines are brand new, I dumped compressor in pail of water with lines attached and no sign of a leak, im thinking its an o ring or a faulty line somewhere

I have done it for many years on problem systems. If I had left any moisture in the system, I'd get ice chips inside.

And yes, I DO leave the system on a vacuum pump for quite awhile. The main reason for the pump is to lower the boiling point of water inside
the system so it boils out.

If you "never" do it, that is fine with me. I do. Been doing it since the late 60s. 50 years plus and have yet to have any problems from it
WHEN a proper vacuum is pulled.

I agree with you JDEM,,I use Nitrogen here,it's cheap,and it lets me go up to 300 PSI on a test to find problem leaks like this one,,I keep a couple tanks here for AC test and for charging accumulators.. also for testing Hydraulic lines..it is handy for all these uses.

If I already had nitrogen in the shop, I would use it but I don't. I used to keep it just to charge John Deere accumulators but no more.

Don't rule out the possibility of the compressor seal being bad even though new. Nitrogen is my first "go to", but florescent dye and will definitely find your leak, especially comp seal.

found the problem, it was the new line the evaporator inlet line where the low pressure switch goes on. defective part, the fitting had a flat spot on it where as it should have been bevelled.

Those kind of thinks can drive you crazy,,Darn it...Glad you found it.