All 3 terminals blown out of scroll.

[ruud-man]

I've been reviewing some of the most common and uncommon causes for this failure.

Any thoughts or experiences?


Best regards...

[4l530]

It happened once when our Service Mgr. went to a fellow's house about 4am and installed a Superboost on a locked up 30 year old compressor. After he left the fusite blew out.
I was there about 7:30am to install a new system :p

[apprentice3]

I had one blow its terminals out last week. The capacitor was bad, so i installed a new capacitor, and as soon as i reset the breaker and started it it blew the terminals off and the refrigerant which was black and contaminated with acid came out of the compressor. The motor ended up being shorted as well. So i guess a short or acid could cause the terminals to blow off

[RoBoTeq]

Most common reason for this is the compressor operated in a vacuum.

[tech_support007]

Originally posted by ruud-man
I've been reviewing some of the most common and uncommon causes for this failure.

Any thoughts or experiences?


Best regards...

Is this a new unit?

[ruud-man]

New unit.

I get a call from a contractor:

Supposedly this was a DOA (scroll stuck-locked rotor). Then the replacement compressor did the same thing (what are the odds?).

Now, to top this, the third compressor runs less than 60 days and blows the terminals.

If this wasn't getting so expensive, I would consider it a comedy of errors.

No mention of checking the run capacitor, eletrical connections, contactor, or supply voltage. When I asked, they think someone may have checked "everything".

Of course the condensing unit is a "lemon". *$(&($^%@*(&%

I guess I'm just venting....

[gerger]

RoBoTeq "Most common reason for this is the compressor operated in a vacuum."


Why does running a comp in a vac cause the terminals to blow out?

[RoBoTeq]

Originally posted by gerger
RoBoTeq "Most common reason for this is the compressor operated in a vacuum."


Why does running a comp in a vac cause the terminals to blow out?

In a vacuum the electrical current strays from the windings burning compressor oil. This causes an extreme pressure issue within microseconds. Once the fusetite blows, oxygen then enters the equation. With oxygenated, superheated oil, you can get some really nasty reactions.

[nickellhead]

WOW thats some really interesting knowledge

[riderman]

RoBoTeq stated:

In a vacuum the electrical current strays from the windings burning compressor oil. This causes an extreme pressure issue within microseconds. Once the fusetite blows, oxygen then enters the equation. With oxygenated, superheated oil, you can get some really nasty reactions.

Is this statement based on fact? I can understand the second half of the paragraph, I'm having trouble understanding the first half. Other than the fact I'm a stupid HO, can you explain this phenomenon? Experience outways school knowledge by far, so this is not ment to be taken as a slam.

[RoBoTeq]

What phenomenum? In a vacuum electrical current strays. Electrical current is hot. Oil is volatile. Add oxygen, oil is more volatile.

I've seen enough blown out fusetite plugs to know it is not a phenomenum but rather a nasty fact.

[riderman]

"Current flow , regardles of the temperature, requires a medium; what is the medium in a perfect vacuum? The perfect vacuum should actually be considered the perfect insulator.
(Look at defination of dielectric constant.)"

Just quoting from one of my books is all.

[Mr Bill]

Hey does that mean if I can get my mind into a perfect vacuum
I will be smarter? :D

[riderman]

LOL

[coolrims]

Goto:

http://www.achrnews.com/CDA/Articles/Service_and_Maintenance/363f3ca0eac5a010VgnVCM100000f932a8c0____

Bottom of page under "System Evacuation"

I recall it was a question used on the EPA Certification Exam. I don't recall which group.

Starting a hermetic compressor under a DEEP vacuum can
cause electrical arcing in the compressor motor windings.

Also this document:

https://www.americantrainco.com/images/uploads/0706EPAWebStudyGuide.pdf

Page 25 under "Deep Vacuum".

[firecontrol]

Mrbillpro
For about a microsecond :)

[firecontrol]

Riderman
There isn't actually a "perfect" vacuum inside the compressor due to the oil that is there. I was taught that oil boils off at approximately 750 microns.

[troyorr]

Called the Corona Effect

[troyorr]

firecontrol, you were taught wrong

[amickracing]

I'm just rambling here..
but you'll never get a perfect vacuum, especially in the field.

What does a typical compressor pull down to? Maybe 10" of vacuum... far from perfect. Throw in some oil in the mix and I can believe the electricty could stray pretty easy from where it should be going.

[riderman]

I'm convinced. Thanks Guy's.

[RoBoTeq]

Compressor oil boils at about 250 microns.

[kim]

A vacuum offers very little resistance to electron flow.

Consider a neon light, flouresent light, TV tube. All have significant electron flow because of the partial vacuum inside.

[short of gas]

On a 3 phase compressor (scroll) the terminals blow out when the compressor runs backwards. Typically after the unit is plugged in and not checked.

[lynn comstock]

I am assuming that the pins blew out of the fusite block. This is not a common failure (probably less than 1 out of 100).

I know about the corona effect and arcing between the pins on the inside of the fusite block. BUT....How did these compressors get into a deep vacuum without a loss of system charge or a complete blockage of the metering device? Nothing was said to indicate that a vacuum ever existed in this case. Also in a deep vacuum, what material creates the extreme pressure to force the pins out of the fusite? If the pressure were system-wide the tubing would likely fail first. The R-22 compressor shell is typically failure tested at 800#.

Since there have been multiple failures (at least 3 in a row). I will suggest that carbon from the previous burnouts has formed a carbon bridge on the inside of the fusite between the pins. This carbon deposit creates a pathway for the arc that damages the pins right at the fusite block. Then the system pressure pushes the pin stubs out of the fusite block. I don't know what caused the bridge on compressor #1 unless this is a condensing unit that was installed on existing system (piping and coil) that was already contaminated by previous compressor failures.

[RoBoTeq]

I would say it is a lot less common then 1 out of 100, but I get your drift Lynn.

What causes the intense pressure is from the arching taking out a terminal and nearly similtaneously injecting air into the superheated oil. Air/oil mixture ignited;;;;BOOM!

TXVs can fail closed, systems can lose refrigerant. Lots of things "can" happen to cause a compressor to go into a vacuum.

[Wild Leg]

Originally posted by lynn comstock

...I will suggest that carbon from the previous burnouts has formed a carbon bridge on the inside of the fusite between the pins...

Or on the outside, in the wiring harness.

If the original wiring harness was re-used, then carbon tracking in the plastic could have caused the subsequent failures.

I would make sure the compressor got a new wiring harness, even if nobody wants to warranty it.

[lynn comstock]

I see how that could happen. About 15 years ago, a tech in our town pressurized a system using oxygen. The top half of the compressor dome broke free from the weld, drove through the top of the package unit's metal top cover and came to rest over 100 feet away. The tech survived with the scare of his life.

Still a problem like a failed TXV is still failed and would be discovered when a replacement compressor is installed. There is no mention of such evidence. The only mode that I could think of where the evidence would come and go is WAX. But I have only seen this once in 50 years, on an R12 walkin. Moisture seems even more unlikely to me.

I would like to know more about the system history and cleanup procedures follwed.

[ruud-man]

I certainly appreciate all the responses. Please keep them coming.

Best regards...