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Finding a leak with vacuum; pre-charge

booksix on Sat June 06, 2009 3:10 AM User is offline

I am attempting to charge an all new R134A system for the first time. I was able to pull right around 30" vacuum on my system but lost it all after about 1-2 hours. I don't want to have to do dye; any way to find the leak under vacuum rather than charging positive pressure with something?

Chick on Sat June 06, 2009 7:32 AM User is offlineView users profile

If you give us a little more information, it may help, make model, what was changed etc.. Why don't you want to use UV dye? Most auto makers use it right from assembly.. As far as finding the leak under vacuum, not unless you can hear it hissing...

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

Voyager97 on Sat June 06, 2009 12:43 PM User is offlineView users profile

Pressure charging with Oxygen-Free Nitrogen is the only reliable way to find a leak.

Think of a reed valve - sucking on it will close the valve, blowing on it will open it. You could hold a perfect vacuum for days, but still leak when the system is charged.



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Vic @ Pennine AutoChill

booksix on Sat June 06, 2009 3:35 PM User is offline

I didn't want to use dye cause I was hoping there was a simpler way without buying extra tools. The car is an '88 Thunderbird with a '89 Mustang engine and matching compressor, '95 Mustang accumulator and an '03 Mustang evaporator core. Most of the system is made up of brand new parts. So, if I go the uv dye route I'm assuming the system needs to be under pressure to force the dye out the leaks. What are my options for charging? I'm looking for things I can get at the local auto store...

Edited: Sat June 06, 2009 at 3:36 PM by booksix

iceman2555 on Sat June 06, 2009 4:03 PM User is offlineView users profile

Why not simply introduce app 1 lb of 134a into the system. This should produce sufficient pressure to test the system.
Unless someone has a very good infra red leak detector...adding nitrogen to the system may not produce the desired results.
This is not a serious issue. The more serious issue is the desire to take short cuts. This action leads to more secondary compressor replacements that one can imagine.
Locate the leak, if it has one, the loss of vacuum may have been the result of leaking manifold fittings or connections.
A vacuum test is not a good indicator of a properly sealed system. The system may maintain vacuum and then leak once pressures are evident.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

booksix on Sat June 06, 2009 4:25 PM User is offline

so, I could take one of my 8oz cans, add it and some dye and use a uv light and the yellow goggles? That's not too bad I guess...

iceman2555 on Sat June 06, 2009 8:43 PM User is offlineView users profile

A better suggestion, add the refrigerant....start the engine...allow to reach N.O.T and then check the system with a good leak detector.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

bohica2xo on Sat June 06, 2009 10:11 PM User is offline

Ok, this is getting confusing.

1) You have a gross leak. Either your manifold connections are bad, or you have a damaged seal in your new components. If it leaks under vacuum, it will leak under pressure too. While some leaks will only show up under pressure, losing vacuum in an hour is a gross leak.

Go over your manifold, connections & test hoses, many times a vacuum leak is not the system at all.

2) Dye can be added to a system that is not charged, simply by pouring it in. Adding dye is always a good plan, it can save you time down the road. There is a reason the factory has made this a habbit for years - it saves them diagnostic time.

3) Once you can get it to hold vacuum, you can charge a few ounces of 134a to pressurize things for leak testing. The static pressure will be higher in a warm engine compartment, and you can checl for leaks with an electronic sniffer. Do NOT run the compressor with less than a full charge.

4) Dye only works if you have a fully charged system. The dye circulates with the oil, and will leak out the same way. VERY handy on a ford full of springlocks.


Find & fix the vacuum leak. If you want to do this under pressure, use 134a. Given the size of your leak, soap bubbles (Big Blu) should show you the leak. It would be faster to use a sniffer if you have one.

Pop a connection apart, and put some dye in it before you charge it - or charge with dyed 134a. I put dye in virtually everything anymore.

B.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

booksix on Sun June 07, 2009 1:24 AM User is offline

Ok, well, when I said the system is new that was a relative term. I meant it WAS new a few years ago and I haven't yet had it fully charged to use. However, about two years ago I had the system mostly charged and it held that charge for well over a year. Since then I've made changes to the car which required a new accumulator, evaporator and line between the accumulator and compressor... I put a 2003 Mustang dash in the car and (stupidly) left the used evaporator in there. I'm thinking that is most likely the source of the leak (it's not the manifold as I pulled vac, disconnected and 45 min later reconnected to find no vac). How could I possibly test just the evaporator core for a leak?

Chick on Sun June 07, 2009 7:08 AM User is offlineView users profile

Leave your manifold hooked up when checking for a vacuum leak, otherwise the vacuum can pull past the service ports (shrader valves)..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

booksix on Sun June 07, 2009 6:37 PM User is offline

that makes sense, because the vacuum will pull the valve open, huh? Well, I only did that after loosing vac with the manifold connected about 3 times... Well, I still don't know what to do cause I think it might be the used evap core but idk how to test just that (nor can I pull the dash to replace right now)...

booksix on Thu June 11, 2009 1:29 AM User is offline

I was thinking about this today and was wondering if my lack of teflon tape (didn't have any at the time) may have allowed the fittings on the hoses to be the source of the leak...? btw, the manifold gauge set is a cheap harbor freight set.

Edited: Thu June 11, 2009 at 1:37 AM by booksix

Dougflas on Thu June 11, 2009 5:37 AM User is offline

Don't use teflon tape at the fittings. Use only new o-rings and spring lock orings for spring lock fittings. Lubricate the orings with refrigerant oil first.

booksix on Thu June 11, 2009 12:20 PM User is offline

Sorry, I'm wondering about the need for teflon tape on the threaded fittings on the manifold gauge set, not anything on the actual a/c system.

HECAT on Thu June 11, 2009 3:35 PM User is offline

Quote
Originally posted by: booksix
How could I possibly test just the evaporator core for a leak?

Disconnect the connections and pull a vacuum on that isolated component.



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booksix on Thu June 11, 2009 4:12 PM User is offline

I don't have the proper fittings to do that reliably... Hmm....? More than anything I'm wondering about the need for Teflon tape on the threaded fittings for the manifold...

mk378 on Thu June 11, 2009 4:19 PM User is offline

They don't need it either. Manifold fittings should seal with flat rubber gaskets, the other end where the car couplers go on may have o-rings instead.

See if your manifold will hold vacuum while disconnected from the car. Of course don't expect it to hold for hours, because there is such a tiny volume there.

booksix on Sun June 14, 2009 3:16 AM User is offline

also, my high side coupler rocks on the fitting quite a bit (low side locks on and doesn't really move). Is this normal? Just trying to think of all the possible sources of leak and can't help but question the cheap gear!


Edit, ok, so I'm trying to test this manifold gauge set and had these issues:

Started pulling vac on the manifold alone. Opened the valves on the manifold and very quickly got to 30" vac. If I twist the high side quick disconnect valve to full clockwise, (to where it would be pushing the schrader valve on the car open) I get good vac BUT if I do the same on the low side I get nothing. I tried twisting the quick disconnect for the low side as far as I could go either way and got nothing at any point... thoughts?

Edited: Sun June 14, 2009 at 3:30 AM by booksix

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