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Check the relay Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Thu, 13 Aug 2009 05:46:42 In Reply to: re: ac compressor cuts out, bob rosen, Wed, 12 Aug 2009 11:56:28 Members do not see ads below this line. - Help Keep This Site Online - Signup |
When the relay contacts get dirty (due to arcing), they build up resistance. Push lots of current through that resistance, and you get heat. As the contacts heat up, the resistance increases, which creates more heat, creating more resistance.... finally, the resistance is high enough that the relay can't pass enough current to pull the clutch in (and drive the fan).
I've seen this before. It can be the contacts internal to the relay, and it can also be the lugs on the bottom of the relay where they fit into the socket.
At a minimum, pull the relay and pop off the cover. Inspect the contacts - if they look chewed up, clean them up with a little fine sandpaper. If they're really chewed up, replace the relay. Spray the relay lugs and socket with contact cleaner. The relay lugs can look fine, but still have a very (very!) thin layer of oxide buildup. Even a fraction of an ohm of resistance can keep the clutch from pulling in.
The reason I don't think it's the fan or the clutch is that you've got a fuse in the system. If the system were pulling more current than the relay can handle (causing it to overheat), the fuse would probably blow at some point. Fuses aren't precision devices, but heat them up long enough and they will blow.
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