On 2014-06-26, notmcguyver wrote:
Why would an apartments central AC units compressors run cap blow up &
start fire of wiring?
a tenants AC went down & that's what I found when I got up on roof. Is
is a lack of maintenance issue?
Based on *my* central AC unit, what *could* happen is that the
cap could either fail open or fail shorted. (Mine failed open). And
every time the compressor tried to run, it would draw *lots* of current
(dim the lights) for perhaps five seconds, until a thermal limiter
opened, and then a few minutes later it would do the same thing. (This
was because there was only the single phase -- not the shifted phase
needed to start the motor, so it was stalled and drawing a lot of
current.
Now -- if the cap shorted instead, it would draw current through
both windings, but with no phase shift, so it would still not start
spinning -- and the current through the cap (especially if it were not a
*full* short) would heat it up, and eventually burst the housing with
boiling oil. Any spark at that time would likely set the oil on fire.
And that thermal switch I *think* is only in series with the
main winding, not with the cap shifted winding, so a shorted cap would
keep drawing current even after the thermal switch opened.
But this is all speculation.
No doubt you don't have three phase available. If you did, you
could run both the compressor and the external cooling fan from three
phase and not have to worry about run caps. (Obviously, the compressor
and the cooling fan would have to be *made* for three phase. :-)
I hope that the fire was confined to inside the housing, and did
not other damage.
I don't know of any maintenance which could have prevented
this -- unless the spade connectors on the cap were corroding and
heating up, and regular inspection might have spotted that.
Perhaps replace the cap proactively every few years?
Hopefully, a professional AC person will chime in to give more
complete information.
Good Luck,
DoN.
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