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UV lamps

Bob on Thu August 27, 2009 12:42 PM User is offlineView users profile

I have a van that has UV dye in the R134a. Have a slight leak and want to track it down. Assuming you need a UV lamp to see the dye. Could you use a black light for this purpose? What wavelength bulb is necessary to see the dye?

Thanks

knightgang on Thu August 27, 2009 10:14 PM User is offline

Yes

NickD on Thu August 27, 2009 10:17 PM User is offline

I still prefer a very sensitive electronic leak detector, under an ounce per year sensitivity, gas can still leak out the higher areas without a trace of oil or dye.

As Chick says, that is just my opinion. (LOL, based on over two weeks of working on AC systems).

mk378 on Thu August 27, 2009 10:36 PM User is offline

Use a fluorescent blacklight. Make sure it has the dark purple glass (a "/BLB" suffix on the bulb type number). There are blacklight tubes for insect traps made of clear glass. These put out the same UV as a blacklight, but also considerable visible light which will make it harder to see the dye. Ideally when looking for UV dye the car should be almost in the dark with the only light from your UV lamp. Yellow "shooting" glasses help a lot too. Do not go without any glasses at all, the blacklight up close is bad for your eyes.

The "blacklight bulbs" that are the same shape as an ordinary 60 watt incandescent bulb and have an incandescent filament are a waste of time. Very little UV output from those.

The wavelength of a fluorescent blacklight is typically rated as 355 nanometers, one of the spectral lines of mercury. UV dye is sensitive to that wavelength. Chemical dyes respond to a range of wavelengths rather than one magic number.

newton5 on Fri August 28, 2009 1:33 AM User is offlineView users profile

As Chick says, that is just my opinion. (LOL, based on over two weeks of working on AC systems).

You mean I only have a week or so to catch up to you, Nick?
I gotta get cracking!

Bob on Fri August 28, 2009 9:12 AM User is offlineView users profile

Thanks for your comments!

GM Tech on Fri August 28, 2009 10:16 AM User is offline

Leak detectors only work IFFFFFFF it is leaking while you are detecting----- leaks can be like farts----only happen randomly.and can be quite dependent on pressure and temp. -- I have documented several bubble popping scenarios- leak detector goes off maybe every 20 minutes for 30 seconds- or so then quiet for another 20 minutes or so.....that is why dye works so well- you don't have to be around- you can go home, have a coffee- check back in a couple of hours---sure a leak detector will find a a constant leak- but if you want to be absolutely sure a joint is leak free-- use the dye.....

I once had a set-up where I used a computer to raise and lower the refrigerant pressure inside the compressor-went from ambient at 80 psi to max of 425 psi- in about 5 hours- - at exactly 261 psi on way up, the belly o-ring would fibulate-- squeak like a mouse-- actually release refrigerant - then be quiet at all other pressures-- then when on way down- pressure decreases from 300- down to 275 etc-- all quiet-- then at 261, again the mouse sound.... I let this repeat for 5 or 6 cycles-- until the refrigerant spray broke my heat lamp.....so go ahead use your leak detectors---but if you want to be sure- you'll use the dye......



Also saying that refrigerant gas can escape without dye and/or oil escaping is just an assumption--I used to think that way- until I accidently had a hole in one of my test balloons- the oil can and does follow the escaping refrigerant- even uphill-- this photo is proof positive.



-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Fri August 28, 2009 at 10:44 AM by GM Tech

NickD on Fri August 28, 2009 12:16 PM User is offline

Soap and water, dyes, and electronic leak detectors are the key leak detection methods, and if using HC's, a match also works. Pressure leak down also determines the existence of a leak but not necessarily where. But does work with component testing and a tank of water. First step is a visual with some historical knowledge of the system, if a system was working fine one day with complete loss of refrigerant the next, pretty much know it's a major leak. Visual requires knowing the difference between AT, brake, PS, engine oil and AC lubricants and determining whether a fluid is seeping out from an AC joint or dripping on from some other source. Signs of refrigerant lubricant is always a sign of a leak. Gut or intuitive feelings also work when particular types of leaks are peculiar to particular types of vehicles. Corrosion in certain areas are highly suspect areas. So have to agree with you may have to use all methods to determine the source of a leak. Although my two week experience has been very void in finding sporadic leaks. But also tend to tap things with my hands in the process. O-ring joints are always suspect as are compressor seals and doesn't hurt to put a wrench on fitting and bolts to make sure they are secure. As are service ports, there, would prefer an electronic.

But what kind of leak are we looking for? One that blows out refrigerant faster than you can put it in, or that extra ounce per year? That also makes a difference. If a system does not have dye in it, you have to put it in first and wait for it to appear.

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