Toyota Repair: A/C in Toyota Avalon, toyota avalon, expansion valve

Question
I have a 1996 Toyota Avalon with an A/C unit that is not working. The unit only blows warm air inside the vehicle. There is no pressure on the low side, even after adding a can of R134a. The compressor is turning on and there is pressure on the high side but I have no guage to check how much. From the information I have been able to research, it appears that the expansion valve could be the problem but I can't get no verification on this.  Could the expansion valve cause this or could there be another problem? I would like to be better informed before spending money on something that I don't need.

Answer
My guess would be as good as yours, yes it could be the expansion valve, it could also be a restriction somewhere else,condensor, receiver drier or even a bad compressor, the most important thing to do first is to read the line pressures with a/c gauges attached and to make sure that the system has the correct amount of freon in it. In this case I would recommend having a professional a/c tech connect gauges and come up with a diagnosis, hopefully the correct one.