Blown start capacitor

[KrisAMS]

The start capacitor literally exploded in the indoor section of our Carrier triple-split (left black crap all over the controls compartment). The serviceman said this in no way harmed the electronics or compressor - and the system does seem to work fine.

So, all I'd like to know is is it correct that nothing has been harmed by this and also what might have caused this to happen?

Regards

[hvacrmedic]

The start capacitor literally exploded in the indoor section of our Carrier triple-split (left black crap all over the controls compartment). The serviceman said this in no way harmed the electronics or compressor - and the system does seem to work fine.

So, all I'd like to know is is it correct that nothing has been harmed by this and also what might have caused this to happen?

Regards

Your capacitor shorted out. Because it's in a can the pressure produced by the electrically vaporized material resulted in a hydraulic bomb. It's not an unusual occurance. The possible causes of the internal short aren't very numerous. One is a manufacturing defect. Two is an overvolting of the capacitor. If number two was the cause, then look forward to another capacitor failure in the near future.

[KrisAMS]

Can you just explain over-volting?

The reversing valve had stuck during the heating season which caused a vapour line lead fuse to blow releasing all the refrigerant. We didn't touch it until the end of the summer when we had the valve changed and the system re-charged. The capacitor blew shortly after this and the new one has been working ever since.

[hvacrmedic]

Can you just explain over-volting?

The reversing valve had stuck during the heating season which caused a vapour line lead fuse to blow releasing all the refrigerant. We didn't touch it until the end of the summer when we had the valve changed and the system re-charged. The capacitor blew shortly after this and the new one has been working ever since.


The capacitor has a voltage rating, either 370 or 440 volts are standard. This is the highest voltage that can develop across the capacitor without risk of dielectric breakdown. Though the unit may be rated at 240 volt, the voltage that develops across the capacitor will be higher than this. Usually around 340 volts.

Under certain adverse conditions the emf of the motor may combine with the input voltage to generate a votage across the capacitor that is higher than its voltage rating. If it runs very long under those conditions the dielectric will break down and POOF the cap swells up, or BOOM it blows up. Running with no refrigerant is one of those adverse conditions. Since that's fixed, I wouldn't worry about the new capacitor.

[KrisAMS]

Well, you are far smarter than me to understand all that! But the last line of your reply came across crystal clear! Thanks.

[marvin]

if it was the start cap it is always a good
idea to replace the start relay with the new cap.

[riderman]

OK, I'm being a smart A@@ here...
Quote:
Under certain adverse conditions the emf of the motor may combine with the input voltage to generate a votage across the capacitor that is higher than its voltage rating Unquote:

Does anyone believe or can explain this? EMF adding to the line voltage, I'm a little confused. OHM's law does apply here:D :))))

[breeze101]

Its for real.

The current that flows through the compressor windings creates a magenetic field of its own which induces a voltage in the very same windings. Its been awhile since i went to school for this and thats all i remember.

I ve had a few of those hard starts blow up where the cardboard in them catches fire. It really makes a mess

[contactor]

If start relay sticks closed. Bye cap. If it happens again, replace relay.

[riderman]

"The current that flows through the compressor windings creates a magenetic field of its own which induces a voltage in the very same windings"

Remember OHM's law..:) The voltage created EMF by itself will not blow the cap. IMHO.

Now a short in the circuit, causing I to increase, will blow a cap. not voltage in and of itself.

[beenthere]

Are you refering to ohm's law for resisteance, or for induction.