Each has their advantages and disadvantages. Find a mechanic and grill him/her on how they would go about finding the leak.
The system has 3- major components and a few gadgets. There is an evaporator, a condenser, and a compressor. The evaporator is under the dash in the passenger compartment. Like the heater core, it looks like a mini radiator and is encased in the air stream. Air goes over it and the heat is exchanged into the refrigerant. The A/C compressor sucks the heat laden refrigerant back to it, compresses the gas back to a liquid, and pushes it through the condenser that is in front of the radiator. The condenser tosses the heat out of the refrigerant and sends it back to the evaporator for another trip. Thanks to the system being in a closed loop, not much leakage is to be expected. Even at the pressures the system sees (200 psi).
The problem areas are the flexible hoses that link the various components. The engine holds onto the compressor and it is powered by the crankshaft. The evaporator and condenser are mounted to the body of the car. Like motor mounts, the flexible hoses undergo stress and strain. Eventually, they will weaken and leak. Remember the pressures we're sending through these? We suggest "looking" at these connections real hard.
DON'T YANK OR PULL ON THEM!! The refrigerant is under static pressure and when it hits the atmosphere it will expand and its temperature will be cold enough to give you INSTANT FROSTBITE wherever it touches or gets near.
THAT WILL PROBABLY BE YOUR HANDS FIRST, THEN YOUR FACE. INCLUDING YOUR EYES!
OK, where were we? The flexible hoses will be found at the compressor and where they go in and out of the evaporator through the firewall on the passenger side of the car (the right side).
Make some real soapy water or get the brush on leak detector. Brush it on the hoses and connections that you can get to and see. There is a filter/drier on the right side of the engine compartment at the battery and radiator area. It should have a little glass portal on the top. (When your done with this exercise, read in your manual how to do a visual check of the system's refrigerant level using this device.)
Soap all the connections up real good. Look for bubble that would indicate a leak. Since your leak is going to be small, and might not be easily accessible, your quick leak check might not yield any positive results.
Another problem area is the condenser. There are a couple of connections there that need attention. The condenser takes the abuse of all of the stuff that gets scooped up off the road into that space. Little rocks, big rocks, sand, etc. chip away at it. The condenser in our '91 with 130+k on it is still holdin' refrigerant, but it looks beat. The bubble type leak detector may not help much here.
To recap, be VERY CAREFUL with the refrigerant. Don't let any of it out or find yourself with a wrench in one hand and eyeballin' the connection that you think you might want to tighten! The system is fairly simple and the irony is the leak may never be found. With a game plan and some knowledge of the layout, you stand a very good chance to succeed.
If somebody gets into your A/C system and changes any part of it, remind them to make sure to evacuate all the moisture, replace the filter drier, and be sure there is the right amount of refrigerant oil in the compressor. (Maybe this is why you're beloved is eating compressors?)
Good hunting
BTW- Running your A/C ea. month (even in the winter) for a few minutes keeps the flexible hoses lubricated and flexible. The oil in the compressor is circulated through the system with the refrigerant.
Contributed by: A&W