AC compressor "venting" refrigerant from compressor
 

I had a dead battery this weekend, and finally got the car to a friend's shop, he was testing the charging system, and with lights on, hood up hooked to the tester, he saw a puff of smoke from the compressor... Looked like a short blast from a Fire extinguisher. He was able to duplicate it with another mechanic and found that the compressor is venting pressure from a valve... Anyone know what causes this? Fans are running, AC is cooling well FYI. 2003 accord 4cyl.

high pressure relief valve is releasing refrigerant. either too much refrigerant in system or a blockage somewhere in the system. did the tech hook up a gage set to see what the pressures are...it will tell alot about the health of the system

In addition to reasons cited above, if cooling fans were not operating, pressures might go high enough to cause a vent. Relief valve protects compressor and other components from damage due to excess pressure. It should be replaced after it vents.

good luck

Had almost the exact same problem except the venting pressure release occurred in my driveway. Ultimately found out it was a AC relay switch that went bad in my fuse box. Had to test all three relays to find the bad one. Not sure what the bad relay controlled but it solved the problem.