I Own A 1999 Lexus Ls400. I Keep Losing Fre-on,only 2to 3 Lbs Of It.
I Had It Checked Out By My Mechanic.he Put In Some Dye To Check For The Leak And Didnt Find Any. He Told Me The Only Other Possiable Thing Is That It Can Be Is The Evaporator. Does Anyone Have Helpful Tips?

 

Replace the evaporator ??

 

Fisrt I dont think you car carries 3 pounds of r134a.
Then you could try one of those leak stoppers that you can add to your system.

Many of them do work if it's a small leak.

 

Sounds stupid but are there screw on caps on the high/low pressure lines (like your tires)? If the tire valve can become clogged without a cap and casue air to be released then it can do it in your A/C system bro. Checking it requires a little water that you pour into the valve stem area - cheap do it yourself option.

 

To add to that, steveski probably hit it on the money. You're using a 'closed' system for AC, meaning the freon isn't consumed anywhere, and in theory it shouldn't leak. Since you said you KEEP losing freon I doubt its your evap. because after a while its just going to clog up and then your AC really won't work. chances are, when you have a clsoed system with an 'undetectable' leak, its your valve core, or a pinhole somewhere else, like in a solder joint or something. Like Steveski said, check those valves.

 

i had the same thing happen, i felt the ac was putting out hot air and it was. 70 degrees, i pumped two lbs of freon in and cold again, it's been 2-3 weeks and the system is still putting out cold air 28-32 degrees.

 

Hmmm I have the same issue. A/C was not cold, got it recharged and it lasted maybe 1.5 months. I am missing one of those caps for the valve (the one you hook r134a can too) Maybe it's leaking there? Do you just pour some water on it to see if it bubbles or what?

 

Yes - it is what I did. A simple idea but you start car with AC on and pour water slowly over valve. It is exceedingly simple yet other valve stems get clogged with debris over time and cause the valve to leak. If it works it will save you money and aggravation.

 

Not to be a knucklehead, but I thought you were supposed to avoid introducing moisture into the AC lines...adding water to check for leaks?

Wouldn't it be better to use some of that AC oil instead?

 

You are right. Water in the lines is never good. He wants to see if the schraeder valve (spelling) like your tire is actually leaking since it has not had a cap on it. Debris can get lodged in the valve without a cap and actually make it leak - it may not the problem but it is real easy to check. He will pour a little water onto the valve to see if there are bubbles. I guess you could use something other than water though. Anything that will bubble will work.

 

isopropyl alcohol should work no? itl dry up if any gets in the AC system

 

That is a great idea Pure since it would evaporate and perhaps clean the dirty area around the valve more than H2O. The valve may not be the source of the leak but it happens with tires, etc.

 

Alcohol? HURRAY!

 

It is the next best thing

 

A lot of suggestions to this problem. All the ideas are great, but why not go with what your mechanic told you in the first place and change the evaporator/ AC Dryer. I have a 95 LS with 173,000 and I'm sure it has never been changed. I have to change mine in the next few days even though I added freon, was checked for leaks and none was found. It blows nothing but hot air. I have asked several mechanics and auto parts stores and they all suggested to change the AC Dryer. There is actually a thread with pictures on how to change it yourself, it's pretty easy. The Dryer cost about $37.00 Advance Auto. You will have recharge your system again after its done. Good luck.