A/C circuit breaker buzzing on startup

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  #1  
Old 08-12-05, 04:05 PM
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Question A/C circuit breaker buzzing on startup

I have a 4 ton air handler (Rheem RBHC) and 1/3 HP compressor (Rheem, not sure on model number but looks like the AJB models on their site) on a 60 amp double pole breaker feed by 6 gauge copper wire. Air handler has a 60 amp breaker on itself. The compressor outside has a fused disconnect.

Every time the A/C starts the breaker in the electrical panel will make a buzz sound. Maybe more like an "ERRRRR" sound to try to put it into words. Occurs for about a second or two and it can be heard through out the house. Has been occurring for a while and the breaker has never tripped.

I decided to replaced the circuit's 60 amp double pole breaker thinking that was the problem but the noise continues. The bus bar and the contacts on the old breaker look ok so I'm out of ideas other then the large start up load.
 
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  #2  
Old 08-16-05, 12:41 PM
badger87
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I've got a different brand air conditioner and I don't know off-hand what size circuit breaker and wire feeds it, but I too get the same kind of buzzing in the service panel when it starts up, so was eager to see a response to this question.

Any ideas anyone?
 
  #3  
Old 08-16-05, 01:12 PM
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As long as the buzzing is only during start-up, I don't think it's a problem. Circuit breakers sometimes buzz when they are near the trip point. The start-up of such a large A/C unit probably pushes the breaker to its limit during normal operation. A motor that size likely draws well over 100A for a brief period before it gets up to speed.

Investigate the A/C unit to make sure that it's clean and that the motor capacitor has not failed; an HVAC repairman can probably check this for you. Either condition could cause excessive start-up current. Does the compressor motor or fan motor need to be lubricated? Perhaps grass clippings and leaves are packed in there or something is rusty?

You tried a different breaker, and you examined the bus bars for damage so I would conclude that this is normal operation. You could try putting a call in to the breaker manufacturer and see what they think.
 
  #4  
Old 08-16-05, 03:44 PM
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I pulled the disconnect on the compressor outside and the handler started without the breaker making the noise. I guess the load is just close to the breaker limit.
 
  #5  
Old 08-16-05, 08:41 PM
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If you know someone with a clamp-type ammeter, you can check what your start-up current is. If you want to investigate further, that would be the next step; or just leave as it and, like mentioned, you're probably okay.
 
  #6  
Old 08-18-05, 01:54 AM
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Maybe.
If the capacitor is going bad on the compressor, that can create excessive current draw.
The compressor maybe straining to start.
-----------------------------------------------------------
Maybe.
Some A/C units have a delay timer for the compressors, with a delay timer the fan may start first than the compressor.
that will lessen the starting current on start ups.
The main reason for the delay timer was to prevent the compressor from restarting immediately, like in a power failure.

The compressor needs time for the back pressure to diminish before a restart or you trip the breakers.
If your unit has a delay timer it maybe bad.
 
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