Honda odysey A/C problem

My 1995 Odysey w/ 173000 miles AC cuts out without notice from time to time for no apparent reason. It can cut out in the midst of operation or it can fail to cool from the start. It will, however, always start to cool again (after failure) when it sits for several hours at rest. The strange part is that the rear AC always works and never cuts out or fails to operate. We had the compressor checked and it's not leaking. The AC blows a frosty 45 degrees when operating correctly. I have been told it is probably an expansion valve malfunctioning. I'd like to know if that sounds feasible before I order the part and start to repair it. Also, what are some of the other possible problems and what are the caveats you'd give an amateur mechanic before attempting the repair himself?