I'm trying to add freon to 1992 Lexus LS 400 where is it located

The first thing to check would be the compressor, check all fuses and see if compressor is running.

i can tell you that most air bag systems develop a leak in the bags and the problem is not fixed inturn the air compressor runs so much to fill leaking bags that it over heats and destroys the compressor. most of the time the compressor fuse will blow, so check fuses first and then compressor. I have never seen a 1992 lexus with air bags.

you remove the compressor and exchange it for a rebuilt one, many companies rebuild them. then you install the rebuilt one and have a shop which does A/C work recharge the whole system.

This job requires special tools and special training. If you lack either, you risk SERIOUS personal injury. Injury comes VERY EASILY!

You need to address oil levels, proper and legal refrigerant recovery, system evacuation, and recharge.

You were planning to also replace the receiver/dryer, correct? It also needs the oil in it measured and incorporated into the amount of oil (in %) that would need to be added. FAILURE to address these and other issues will guarantee premature system failure and likely compressor damage.

Take this job to a qualified shop.

Sorry

R12 is not sold no longer so look on the compressor for a tag of what freon to use. Conversions kits are sold for older cars to use R134a

Here is a diagram that should help you out.

some of these freon have environmental restriction check with an a/c mechanic

there is no common place to check for leak on this car. but i have done alot of evaps in dash.
the compressors.lines.and condensors will all leak sooner or later. the best way to find your leak is to install dye and recharge system and look for leak in a few days with uv light and glasses.you will find the leak. sometimes if leak is bad enough on the evap. you can see it coming out of the drain hole oh fire wall.

The fuel filter is located under the vehicle on the left side before the rear axle.

a/c tripping relay should be located between the switch and the compressor which is the correct location of a relay

First check if the compressor comes on at all when you push the A/C button inside the car while it running. if the RPMs don't move at all, it's probably not coming on.

Also, check all the fuses and make sure they are okay. Your user manuall will give you the location of the fuse.

Next, check the freon level. When there is not enough freon in the system, it will automatically keep the compressor turned off so it doesn't burn it up. One way to see is to add some freon to your system and see if it kicks the compressor on. You can buy a can of freon at any walmart, and you just need a hose to hook up to your "low side" on A/C system and add the freon while the car is running and the A/C is turned on. You will hear it "kick on" when it has enough pressure in the system.

If that works, and a few days go by and it quits, you probably have a leak somewhere.