# troubleshooting a/c circuit



## goldinc413 (Jul 30, 2014)

A restaurant owner called and said he had a weak breaker (3phase) and needed it changed. (His heat and air guy told him it was weak.) I sent a guy with twice my experience out to look at it. Upon arrival he found the breaker in the on position, he checked the voltage and it was correct. The workers told him they had not had problems with the breaker tripping. They said it was something on the roof. So he went up on the roof and checked voltage at the disconnect. It was correct. He opened the unit and the voltage was correct. He pushed a contactor in and it fired right up. My guy called the owner and said there was nothing wrong with the circuit. Of coarse the owner was not impressed with this since this was not what the heat and air guy said. After thinking it over the owner made an appointment and had us meet the a/c guy to figure it out together. My guy showed him what he found and that it was something in the circuit board. Today I found out that after my guy left, the a/c guy went and changed the breaker and apparently the problem is fixed. Now I've never had a situation like this and I'm seeking opinions on if, how or why this is possible? If the voltage was correct then why wouldn't it work? Can a weak breaker not allow enough amps for it to start? Please help.


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## Bad Electrician (May 20, 2014)

Unless your electrician ran the AC and did an FOP on the CB and then tested voltage at the panel and AC he missed something or it could be FM.............................FREAKING MAGIC?


Checking voltage at no load was his mistake. He needed to check it no load and loaded.


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## FlyingSparks (Dec 10, 2012)

Bad Electrician said:


> Unless your electrician ran the AC and did an FOP on the CB and then tested voltage at the panel and AC he missed something or it could be FM.............................FREAKING MAGIC?
> 
> 
> Checking voltage at no load was his mistake. He needed to check it no load and loaded.


I'd have to agree, testing under load is a standard troubleshooting procedure (with the proper PPE of course).


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## dronai (Apr 11, 2011)

goldinc413 said:


> Of coarse the owner was not impressed with this since this was not what the heat and air guy said. After thinking it over the owner made an appointment and had us meet the a/c guy to figure it out together. My guy showed him what he found and that it was something in the circuit board. Today I found out that after my guy left, the a/c guy went and changed the breaker and apparently the problem is fixed. Now I've never had a situation like this and I'm seeking opinions on if, how or why this is possible? If the voltage was correct then why wouldn't it work? Can a weak breaker not allow enough amps for it to start? Please help.


The AC guy was smart, Your guy said "it was something in the circuit board" huh ???


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## JRaef (Mar 23, 2009)

"Weak" breaker... riiiiiight.

That is a BS term, there is no such thing. A breaker may be _worn out_ because it has tripped so many times that it fails to hold in any more, that happens. But just blaming this on a "weak" breaker and replacing it does NOT fix the real problem, it just kicks the can down the road. The REAL problem is, why is the breaker tripping so much that it has worn out? 

By the way, the HVAC guy may have changed the breaker, but only AFTER he fixed his REAL problem, which he didn't want anyone to know about. So there may have been nothing wrong with the breaker at all!


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## Bad Electrician (May 20, 2014)

JRaef

As you know

Breakers can have internal or external connection issues or bad contacts (which is a connection issue), under load the CB may not pass current.


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## dronai (Apr 11, 2011)

goldinc413 said:


> A restaurant owner called and said he had a weak breaker (3phase) and needed it changed. (His heat and air guy told him it was weak.) help.


 Right there, the expert said it was the breaker, and it needed to be changed ! Change it, then charge, and if the problem reoccurs, you were instructed by the AC expert. Then next service call proceed with troubleshooting, but the AC guy should be the one doing this not the electrician unless you are qualified. My opinion of course.


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## goldinc413 (Jul 30, 2014)

I appreciate the feedback and tips. It's disappointing to me that we let the them down on solving the problem. It is in the back of my mind whether the a/c guy fixed something else as well. I would have thought with the getting the "right" voltage it would have at least been attempting to run. Live and learn. Thanks again!


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## Bad Electrician (May 20, 2014)

goldinc413 said:


> I appreciate the feedback and tips. It's disappointing to me that we let the them down on solving the problem. It is in the back of my mind whether the a/c guy fixed something else as well. I would have thought with the getting the "right" voltage it would have at least been attempting to run. Live and learn. Thanks again!


Not trying to beat a dead horse, but it takes a complete investigation, overlook one step and you may miss the problem. 

At least if your electrician had done the load voltage test you would have a leg to stand on with the restaurant in your defense of your trouble shooting. We TRY to train our employees to never walk away from a problem until they know the answer. If they cannot locate the problem I drop what I am doing and head there.


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## power (Feb 27, 2012)

We have experienced this as well. HVAC crews diagnose a problem, and they recommend the replacement of the breaker to the owner. And sometimes the HVAC technician is correct! Most experienced HVAC techs have volt/amp meters and will check for faulty compressors before encouraging further involvement by electricians.

There is something fishy about your technician's claim about the circuit board. A faulty circuit board would hardly dump a 3-pole breaker. Circuit boards are electrically supplied by a control transformer, which is likely fused in the rooftop unit. 

However, while I too object to the term "weak" circuit breakers, I do understand the intent of the term. Breakers can be shipped mis-produced, and thereby trip too soon. Some existing breakers that have been used as switches can also begin to nuisance trip. Perhaps this facility has been de-energizing the roof-top unit at night for energy savings rather than back/up-setting the t-stat. Perhaps the mounting screws of the existing 3-pole breaker were loose, heat was generated, and this heat conducted itself into the breaker's chassis, thus encouraging tripping? 

So in a nutshell, the HVAC mechanic may have been right in his diagnosis, but he shouldn't have changed the breaker himself.


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## BillyGibson (Aug 4, 2014)

I was sad to hear that an amprobe wasn't used in diagnosing a "weak breaker." Additionally I have to say I don't mind that term. I knew exactly the symptoms the HVAC guy described with it. 20a breaker trips at 13a.... "weak breaker" sometimes happens... at least sometimes I have seen it...


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