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Does the AC Clutch have a supression diode built-in? Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 26 May 2005 04:47:47
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Someone contacted me with a AC relay problem - burned contacts. I've seen some badly pitted AC relay contacts causing intermittent AC operation, but his pictures showed a pretty badly burned relay.
In schematics for older 9000's ('88), there is a supression diode in the wiring across the AC clutch. It is wired in 'backwards' (anode to ground), and provides a current path for clutch current when the relay opens - pretty common for highly-inductive DC loads.
I Don't see the diode in schematics for later cars - '92 and up. I assume that there is a diode integral to the clutch. Does anybody know that for sure? I could see that a blown diode would rapidly kill AC relays.
There is no good way to test the integrity (or even presence) of the diode - because the clutch coil is low impedance, you'd need to pass at least 250 ma through the coil in reverse to see if the diode is there - the diode range on most meters only provides a few ma.
And if for some unknown reason they don't include a supression diode, I could see adding one externally to prolong the life of AC relay contacts.
posted by 192.249....
, Thu, 26 May 2005 04:47:47 <-- Viewing This Message
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