chances are with the compressor that hot the windings were on the way out and the overload was the only reason they didnt go before you got there. sooner or later it would have failed and boom anyway. if people would just relize when the house starts to get hot and they make the call turn the unit off then. but they dont and just let it run hopeing it starts to work by some act of god. had one once the coust called at 10pm and his wife could not breath assma. he said he kept turning it down since noon time and it just wouldnt get cold. the compressor was hot as ever when i got there and on over load. hosed it down till it was cool. found run cap was bad exploded. replaced cap checked the windings fired it up. was checking the unit over and the terminals let loose. what a fire works show it was. it would seem to me only that the matereil used to hold the terminals get to hot and break down to a point it can no longer hold up to the presure and let go. have seen a lot of blown terminals but that was the only time i was there when it happened. hope never to see it again iether
The way it has been explained to me by a Copeland engineer is that the unit either loses charge or due to a restriction the compressor goes into a vacuum. This causes high internal temperatures and electrical arching that happen faster then the safety shutoffs can react.
Air can either enter the system due to a leak in the low side of the system or directly after a compressor terminal has burned through. Either way it is correct that oxygen must be present before an explosion can take place.
I have most likely seen this more often then others due to my position of having to investigate this sort of failure. The company I repped for allowed me to take affirmative actions to get a new system installed as fast as possible with no cost to the consumer and as little cost to the contractor as possible no matter what the circumstances were that could have caused the problem. When this occurs, it is always a mess. If a homeowner was present when it occured, there is a need to make that homeowner feel comfortable with a replacement unit.
As I read Robo's reply to this post, I was reminded of a repair I did last year on A Trane Intellipak. I pumped the charge into the condenser as I've done on other units many times. And to get as much refrigerant in to the high side as I could, I let the low side go into a slight vac. Two days later at a copeland seminar, I found out that your not suposed to do that with a scroll for the reason Robo stated about the arcing in a vac. I was lucky nothing happened.this site is a great source of info!I consider it continuing education. Thank You Robo and many others here for sharing.
Originally posted by RoBoTeq I guess how well those dust/moisture covers stay on depends more on the holding clip. I know there are a lot of things we are supposed to do for safety, but how many of them do we really do? I can't ever remember seeing any tech put that cover back on until he was ready to button things up.
When I was in school, we got shown a safety film about the importance of never powering up a compressor without the terminal cover in place. The film was kinda gruesome and over the top, but I took it seriously.
My very first summer doing service work I had a service call on an old Lennox HS9 condensor that "keeps tripping breaker".
I didn't find any shorts to ground and the winding to winding resistances looked ok, but the compressor kept making a wierd sound for a few seconds before tripping the breaker.
Having seen a bad potential relay cause problems that seemed similar, I removed the wiring to it and tried starting the compressor again.
The compressor made a "chuchunk" noise and then the terminal block blew out. I was about 18" from it with it pointing directly at me. I was holding my Amprobe ACD-10 that was clamped around the start leed about 2 inches below the terminals.
I didn't suffer any injury because I put the plastic terminal cover back on after ohming the compressor out and it stayed in place and directed everythng out the bottom of the cover. It did blow one of the jaws off my meter though.
Actually, I did suffer some injury. I probably broke the world record for the backwards broad jump, and bruised my arse on a rock when I landed.
Never power up a compressor with the terminal cover off, especially if you are diagnosing a suspected electrical problem with the compressor.
[Edited by mark beiser on 05-16-2005 at 11:13 AM]
If more government is the answer, then it's a really stupid question.