A/C leak detector,,,?

Howdy,,,,,,I got a very small leak on the A/C on the 92 Ranger that I just cannot find to repair it. It will take bout a week to leak bout a can of the R134. What is puzzling is,, I evacuated the system to 10" and it held there for bout 3 hours before I added 1 1/2 cans of Freon. It leaked out after a week. I have added 2 different kinds of detector but it never shows up where I can see it.
What do others use for detecting,,,??? Thanks

Schrader valve leaking?

OK,,Stan,,,,,,Say,,,you got an idee where I might rent a scuba outfit,,,,???
Hey Sho-Man1 that's a great idea,,!!! Actually,,,there is a shraeder valve on the high side that points straight up and was full of gookies and I dug around it with my knife,,chit,,I mighta messed it up,,?? Gonna go put another can of Freon in the trk and check Both of the shraeder valves. I wonder if those are the same as the valves on trk tubes,,??
Hey Steve,,you remember what brand of leak sealer you used??

I agree with Stan's idea! I drove my 3/4 Chevy today, hit the AC button and was basking in nice cold air all day. I haven't touched the AC since I bought it 3-4 years ago. (it's a '98). (poke,poke,poke)

I gots a sharp corn knife, I could trim up some of them hoses for you!

my mechanic has a little beeper thingy he checks lines and the system with

Joey those valves ARE regular Schrader valves from tire valves!

That sealant stuff WILL eventually plug up the screen or orifice in the expansion valve.  If air gets in the system I have seen that stuff build up, get hard and at first I thought it was a pencil in the system, not to mention stink to high heaven.  The only leak detector I use or recommend is a  H10, made by Mars, Bacharach, or GE.  I personally use the 110 volt version, but they also have battery ones.  For leak checking, I use Nitrogen at a pressure of 110 to 119lbs for a minimum of 3 hours, these pressures are much easier to see a leak on the low side gauge.  If the leak is hard to find you can split the system and start checking each section by sealing it off.  Now for vacuum, inches of vacuum = spit.  I change oil in my vacuum pump after every evacuation, I spend a lot on oil but I also pull my systems down to 50 to 100 microns.  For automotive I would recommend 350 to 400 microns, bear in mind, atmospheric pressure is 760,000 microns, at 10" vacuum, you are still at 760,000.

don't you have a big ole nose? gits down there and sniff! (poke,poke)

Joe the easiest way to find the leak is to pressurize the system, then spray everything in sight with Dawn dish soap and water. Of course there will be some places you can't get to so it might be you would need a tester in those cases The schraeder valves are different. They will physically fit but the little piece that sticks out of the middle is shorter on the valve stem ones, so your gauges will not depress them, not will anything else using this kind of port. You need to pick up the special tool to remove or tighten them because one that fits a car tire for instance isn't long enough to reach the valve. 

Did you test WITH the engine RUNNING ??? OK, maybe that sounds daft BUT vibration can 'loosen' up and O-ring seal and pisssst , there goes $100 of freon.
I learned that on an 88 Aerostar, idiot engineers at Ford replaced GOOD fittings with cheap aluminum and 2 o-rings...only took 1 to fail to lose the gas...

When I wants to check my AC for leaks, I parks it onna' clean concrete slab, and come back inna mornin'!