How to add UV dye to A/C system


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Old 05-09-14, 04:49 AM
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How to add UV dye to A/C system

What is the proper procedure for adding the UV dye that comes in a separate vial (not the kind included with R-134a)?

Here's where I'd get stuck: Say the system is drawn down and shows a nice vacuum holding on the manifold gauge. I pour the proper amount of UV dye into the yellow service hose on the gauge set and connect the R-134a can. But now I need to briefly loosen the service hose to purge the air from the line. If I do that I lose most of my dye, squirted out everywhere along with the purged air. (Right?)

It seems I'm stuck with two choices: Having a small amount of air in my system or not having hardly any dye in there. Which one I pick I guess depends on the vacuum test. Next time I'll buy it with the dye in the can.
 
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Old 05-09-14, 12:31 PM
W
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They make a fitting to do this , but I do not have one .

Worse comes to worse , you COULD , while you still have a vacuum in the system , remove the hose from the vacuum pump ,. Either pour some in the hose as you described . Or stick the end of the hose in some oil ( containing dye ) and open the manifold low pressure valve enough to let it slurp up the dye / oil .

To be safe , after it has " digested " the oil / dye , vacuum it down again .

A pain , I know . But you asked .......

God bless
Wyr
 
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Old 05-09-14, 01:18 PM
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while you still have a vacuum in the system , remove the hose from the vacuum pump ,. Either pour some in the hose as you described
Wouldn't I instantly lose my vacuum then? But I believe there's a shraeder on the pump side of the service hose, so I wouldn't lose my vacuum. But in that case I couldn't pour dye in that end either, because it would have nowhere to go.

I like the idea of submerging the hose in the dye. I'd just need to rig up something where I could press on the valve whilst it was submerged, like a nail bent into a tight U shape or something. Honestly I've not used this brand new manifold set of mine so I'm not even sure if there is a shraeder on it. I'll be finding out shortly.

I'm beginning to think this is more trouble than it's worth. If the vacuum shows a leak, then a little air in there for a couple hours won't hurt much. And if there's no leak then I guess I don't really need the dye in there at present.

I'm interested in this fitting you mentioned. Won't help me with today's festivities but I've got other cars to do also.
 
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Old 05-09-14, 01:52 PM
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WyrTwister-

After getting the gauges out and on the car... ah hah, now I think I see what you were saying! The end with the schrader is large enough for about a thimbleful of dye. I just fill that while holding the thing perfectly still and upright, blip the schrader with a nail, let it suck in a small amount (but not all), rinse and repeat. As long as it doesn't all get sucked in dry then no air should get in.

Thanks!
 
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Old 05-09-14, 03:06 PM
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You need another tool. An oil/dye injector.

A C Air Conditioner Oil Injector for R134a Systems | eBay

When I was in shop I had a small container (about 4 oz.) that fit in the suction line on gauges and had a valve. One end would unscrew for pouring in the dye and oil, the threaded cap had an O-ring for sealing. Get system under vacuum, pour in dye and oil, close container, and open valve on container to inject dye into system. Fluorescent dye worked better with a little oil to get it into system.
Charge system and run for awhile, then check with "Black light".
You can inject the oil/dye under pressure (don't need a vacuum) from your 134a supply connected to the injector.
Worked for me.

RR
 

Last edited by Rough Rooster; 05-09-14 at 03:22 PM.
 

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