Q: Why does AC quit after about 15 minutes? on 2000 Toyota Echo

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I had the AC checked, refrigrant added w/dye. It worked about 3 wks. Now runs OK for 15/20 minutes, then blows warm air. Toyota cannot find any loss of refrigrant or trace of dye leaks. Could it be the electical system? If not, what are the other things that could be wrong?
(2) Answers
It can be electrical. As electrical components warm up and get hot they can fail. As they cool down they will start working normally again. Your problem can be several things. I suggest you have someone check for power to the a/c compressor when the A/C stops working, if it has voltage and is not working, the compressor clutch is failing. If it loses the voltage signal then the system will need to be diagnosed further.
the compressor clutch is electrical/magnetic and will get rusty. Clean the rust from the two surfaces and see how that works.You can loosen the plastic splash pan under the front of the car and pull it back to access the pulley. Remove the outer half and clean the inner half on the car. Hope this helps.