AC Unit makes lights flicker when it starts

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  #1  
Old 08-19-14, 10:11 AM
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AC Unit makes lights flicker when it starts

I just had a new HVAC system installed a couple of days ago. Today I noticed the lights flicker when the AC unit kicks on. Now the flicker only seems to affect the incandescent lights and not the others (LED, CFL). After searching online a bit I read somewhere that incandescent lights are very sensitive to voltage drops and even small voltage drops will cause them to flicker.

I was going to call the HVAC company to see what they say about it, but before I waste their time and mine I wanted to see what everyone else thought about this. Is it something I should be concerned about or is it really no big deal. Also I assume the importance of the voltage drop depends on the amount of the volts that I am losing. Is there a way I could test this on my own with a multimeter or other similar tool?

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Old 08-19-14, 10:27 AM
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Lights flickering when a central A/C system starts up is perfectly normal. The load of the compressor, condensor fan and usually the blower all coming on at the same time is incredible.

One factor is - how far away from the utility transformer are you ? The further the distance the greater the flickering.

You can test before and after voltages but they won't tell you a lot. Make sure the house voltage is up near 120/240vac.
 
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Old 08-19-14, 10:33 AM
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I just used to a multimeter to test an outlet while the AC unit was off. It was showing 121 Volts. I left it plugged in and turned on the AC unit. When it kicked on the Volts dropped to 117 and quickly went back up to 121. Is this a proper way to test voltage drop? I don't know how far I am away from the transformer, but I can go outside and check.
 
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Old 08-19-14, 10:47 AM
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A five volt momentary drop is not excessive based on that load.
 
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Old 08-19-14, 10:50 AM
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Okay I didn't think that was much of a drop. Also I am only about 50ft away from the nearest transformer.

Thank you for the quick response.
 
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Old 08-19-14, 10:54 AM
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Nobody here can tell you with certainty if it is normal or not without evaluating the installation..

However, if its just a momentary blip in the lights what you are likely seeing is normal voltage drop. Plus some folks are more sensitive to flicker and light output. The inrush current of your new scroll compressor is a serious draw but just for the split second it gets to speed. On an older unit one might consider a hard start kit to lessen the flicker but even then it would be very hard to totally eliminate it.

With that said, you just paid big bucks for your AC so I would not hesitate calling the company back out to take a look... Did the HVAC company install or modify the circuit for the AC?
 
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Old 08-19-14, 11:29 AM
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They installed a new breaker for the unit. I have tested it a couple times now with different outlets and the biggest drop in voltage has only been 5 volts for just a split second. I have no problem calling them, I just like to know a little bit about what what I'm calling them for.
 
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Old 08-20-14, 12:29 AM
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I just like to know a little bit about what what I'm calling them for.
That makes two of us.
 
  #9  
Old 08-20-14, 05:57 AM
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Have you called your UTILITY CO. to check their connections? Maybe your transformer is loaded up or you have a bad connection. They might even go as far as putting a recording device on your service. Does your lights flicker when your neighbors AC starts?

Have you had an ELECTRICIAN assure all your connections are tight at the meter socket, panel etc? Is your service balanced for the loads present?
 
  #10  
Old 08-20-14, 06:18 AM
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If your old unit didn't make the lights flicker the new unit was probably sold as higher efficiency and you are finding out what that really means.
 
  #11  
Old 08-20-14, 07:58 AM
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I just had a new HVAC system installed a couple of days ago.
Was this a full replacement with replacement of a-c unit too? Did you have a central a-c unit before?
 
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