Air Conditioning - Is This Possible?

Compressor is a carlyle 15 HP - Carrier Heat Pump - This unit contains an internal unit 40 HAC Breaker (34 close tolorance type). It keeps tripping even when the amps on each phase are as follows : 29.6 - 30.4 - 31.0

RLA= 29.6

The charge/Superheat/Subcooling are textbook.

Question is: If the contactor is pitted but no voltage drop accross any contact(no abnormal resistance added) - could it (The pitted contactor)cause the breaker to heat and trip?

* I obviously called the breaker bad.

*Another (very qualified tech within my company) believes the pitted contactor could cause this. ...I find it hard to believe (No VD at any contact) which would (if there was a VD)cause a voltage imbalance which the close tolorance CB would catch and heat up. Wouldnt the voltage drop be reflected in the amp draw? The Amp draw is textbook RLA. I dont agree that a pitted contactor with no VD can cause this overheating of the breaker. I believe it is solo a breaker problem

Please give me some input on this - If it is possible -could a pitted contact cause the breaker to trip? - Explain (technically)exactly how this could cause a fault such as this.

Thanks in advance!

David

Here is one very good answer from a fellow technician I received but (unfortunately) doesnt fit the problem as I state below.

"On a few rare occasions I have seen 3 phase breakers trip when the contactor tried to open, in these cases the contactor would open one of the phases and the motor would be single phasing because the armature of the contactor would not drop down quickly enough to open the other two phases before the breaker kicked out.

This condition is rare and hard to catch unless you are standing right there and realize that the breaker trips when the unit is cycling off and not cycling on or running.

This may not be the cause on your unit, but if a new breaker does not solve the problem it is a cause that you can investigate, watch the current while you cycle the unit off."

(My answer to that is)...

The reason this (Although it is a really good answer)couldnt be true, is the store (Aeropostle) was hot 85 degree's inside - The Tstat would not have been satisfied for at least some time - The (close tolorance internal type)breaker was tripping within 5-10 minutes each time I restarted the system - I simply checked all the current and voltage drops - The breaker seemed to be heating up - Couldnt determine anything but the breaker being bad.

The next time it trips immediately open the power source and do a touch test for hot connections on bottom and top of breaker terminals. Also check for tightness of those connections?
Would there happen to be two small signal wires going into the breaker body. I have seen breakers that received signals from other thermal/current devices etc that would trip the main breaker, LOL Tom

I agree about the contactor. Pitting would look more like a voltage drop. In order to trip the breaker you would need to have contact chatter, constantly making and breaking to heat up the breaker.

Tom, I've usually seen those type of breakers on Trane units. Don't think I've ever seen on any others.

Real, I've never seen a properly charge unit with compressor running at rated RLA. Have seen properly charged compressors slowly start drawing more and more amps until it pops breaker.

I would look more at the comp. Also if a packaged unit, wiegh the charge in and out.

What is model? I'd like to take a look at it.

Chris

Three-phase is out of my (current)league. But have you measured for heat at breakers with an infrared gun? Could breaker have weakened over time with no other problem?

I recently had to replace my 240 volt water heater double breaker that I amp tested draw at 16 amps (20 amp 2-pole) and it got real hot and tripped all the time. Now the new one I put in fixed it, and now the breaker only gets warm - not hot.

Also, with single phase fuses at least, the contacts in the box themselves can go bad, generate heat right there by the fuse or, breaker and cause it to trip.

Regarding pitting, or any other downsizing for the electric current to cross, - how can that increase the heat or amps to blow the breaker? Or, in three-phase would this maybe create a heavier amp shift to the other two phases? In single phase though, all that could happen is if amp draw were more than the pits could handle, that you'd likely get a melt down at area of the pitting. JMO

The guys over in the electrical forum may enjoy this question if you posted it there.

Voltage, current and resistance are all interrelated -- you can't change one without changing another. Current is equal to voltage divided by resistance (commonly written as I = v / r). This makes intuitive sense: If you increase the pressure working on electric charge or decrease the resistance, more charge will flow. If you decrease pressure or increase resistance, less charge will flow. To learn more, check out How Electricity Works. ie...http://electronics.howstuffworks.com/circuit-breaker.htm


Bad contact means more resistance - more resistance means less current.... lol Why would a breaker trip on less current. one phase or 3 phase....

Your right, guess you have it figured out. Case closed?

.... In order to trip the breaker you would need to have contact chatter, constantly making and breaking to heat up the breaker......

Chris

Probably many people would never even think of that possibilty. If that say were the cause of someone's problem, could this be occuring and yet not be heard?, if a person reset the breaker next to the unit doing this? Or would something like a big compressor then be making all kinds of on/off clunk sounds when trying to energize/denergize? Or does this occur so rapidly (this chatter) that the compressor does not even have time to react yet?

As was already suggested, an infrared thermometer is one of the best electrical troubleshooting tools going.
If you had an infrared thermometer and a high voltage megohmeter it would be like having a refrigeration crystal ball.

I'd still like the unit and compressor model #'s are. With 29.6 RLA, I figure the MCC would be aroung 46 which is higher than the 40A breaker given.

Looked through my Carlyle Service book and didn't see any 15 HP comps with 29.6 RLA.

Carrier usually uses 06D but have runn across a couple 06E models.

Guess we'll never know.

I'd still like the unit and compressor model #'s are. With 29.6 RLA, I figure the MCC would be aroung 46 which is higher than the 40A breaker given.

Looked through my Carlyle Service book and didn't see any 15 HP comps with 29.6 RLA.

Carrier usually uses 06D but have runn across a couple 06E models.

Guess we'll never know.

Ill get the model numbers for ya - Its in my service truck...lol Oh, btw, great info here. I did find out though that motor dynamics are different than fixed load dynamics on current, resistance, and voltage - will explain later...

*"an infrared thermometer is one of the best electrical troubleshooting tools going." Great point!

Takes over 5 days to get to you van and a slip of paper with model numbers?

Must be a very nice job to have.