Aircon Problem

[sqcamry2003]

My ride is coming 3 yrs old and clocked 115,000 km. Actual usage on aircon could be easily 50% higher since I indulged heavily on ICE and there r plenty of traffic jams at this part of the world.
So far only thing done on the aircon is replacement of air filter and expansion valve (and gas, of course).
About a year back the aircon went into FRESH mode (normally CIRCULATION mode) with AC light blinking. Off/on the aircon reset the problem.
Recently this problem occurs more frequently. Still manage to rest it by off/on the aircon but is irritating.
Any1 has experienced similar problem?
Any idea what would (or which sensor that would) trigger such warning?
The Manual says go to workshop but my workshop is not able to diagnos the problem, since the aircon seems to still work fine.
All input / suggestion wellcome.

[drunken_panda]

Could be a bad belt. When I got the belt wet, the AC cut out and the light started to blink. I cycled it on and off and it worked.