capacitor life - causes of ignition

[fmsaldarriaga]

I am interested in learning the mechanism by which a 2.5 ton a/c window unit with a 40 MFD +10/-5% run capacitor ignited. The capacitor was encased in a plastic housing instead of a metal one. The lower section swelled and burst inner material which was like expanding foam. The construction of the capacitor is unknown to me.
WOuld anyone there know how these capacitors work and how is that the heat evacuation or cooling could have been ineficient to cause a fire.

[chemi-cool]

Life span of capacitors is a mystery, they can last for a long time and they can last for a short time.
Make sure all the wires connections are tight and none of them is getting hot.

http://electronics.howstuffworks.com/capacitor.htm

[martinw58]

if the comp has a relay check it is working corectly

[coolflow]

you could allways buy one and hit it with a hammer to spill its gutts and then you will know and can let us know too !! best €5 spent on education i say..

[mikeref]

Maybe capacitor failed due to power fluctuations, causing compressor to work harder or compressor is working in high load conditions. Possible capacitor is not correct rating or just faulty.

[desA]

An extreme power surge put paid to my folks' washing machine capacitor the other day - blew in spectacular fashion. Variable incoming power can be a nasty.

[mikeref]

An extreme power surge put paid to my folks' washing machine capacitor the other day - blew in spectacular fashion. Variable incoming power can be a nasty.
Hi desA.. my capacitors(start and run) did the same on an a/c. Soft start was faulty and start cap left its case while run bulged, cracked and grey matter appeared. I was not there for the show, just the cleanup.:eek:.. Mike.