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Old 06-25-2011, 01:47 PM   #1
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Lights dim when A/C compressor kicks on


Hi,
I just had a new central air system installed in my house. It’s a Heil system, with a 3 ton compressor. Whenever the compressor starts up, the lights in my house dim a little, very briefly. I had my electrician come back and look at it, and he checked all the connections for tightness, and the voltages and current. I have a fairly new 200AMP service. The voltage at the unit was consistently being 241-243 volts. It drops 2 volts at startup. He also measured the current at startup, and he measured 110AMPs. That’s quite a bit larger than the 77 AMPS written on the compressor label for ‘LRA’ (Locked Rotor Amps). He wasn’t sure if that could be causing the dimming or not (possibly a bad or weak startup capacitor?). He suggested having my installer call Heil to see if the 110AMPS is within spec. He also suggested having the power company check the taps and neutral connection at the pole.

Has anyone else had a problem with lights dimming when an A/C system starts up? The electrician said it really shouldn’t be happening with my setup (new system, good 200AMP service, etc..). Any ideas or suggestions?

Thanks very much.
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Old 06-25-2011, 02:05 PM   #2
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Lights dim when A/C compressor kicks on


that dimming is the locked rotor for a "milli seconds" on start ups your condenser is 208/230 from both sides of the street feed on the condenser breaker...washer/micro do the same but not as noticed as they are 115Vs and on one side of that panel 115Vs not 208/230 as that condenser only noticed at night more....obviously just write it off as there goes the cooling running..the RLA is the compressor running amperage and usuallly runs half that on a low humid day but 75% on a baker where you can't move your running the unit is the bill but they bang you on that LOcked roToR on start...thats why they have starters in cars
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Last edited by biggles; 06-25-2011 at 02:11 PM.
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Old 06-25-2011, 04:09 PM   #3
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Lights dim when A/C compressor kicks on


Biggles, I did not understand anything you just said.


But yes, lights dimming is normal, if you ever plugged a light into the same outlet of a refrigerator you would see the same thing as well (sometimes all over the house). I actually like it when they dim, you know the air just came on.
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Old 06-25-2011, 08:05 PM   #4
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Lights dim when A/C compressor kicks on


Have your installer put a 5-2-1 hard start kit on or have him order a factory hard start kit(same thing). The lights should not dim on a new install but it does happen once in a great while and the hard start kit solves the problem.
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Old 06-26-2011, 06:06 AM   #5
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Lights dim when A/C compressor kicks on


check if the stat has an adjustable time off for the cooling so it has time to equalize or install an adjustable time delay on the incoming 24V wire within the condenser..i would do the hard start as a last thing especially on a new unit...go with the time delay.a hard start pushes the windings on the compressor and could lead to compressor burn outs and cooked freon$$$$$ http://www.bestbuyheatingandaircondi..._Code=REL203AA
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Old 06-26-2011, 06:29 AM   #6
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Lights dim when A/C compressor kicks on


Any induction motor will cause lights to dim briefly during the initial startup.
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Old 06-26-2011, 06:33 AM   #7
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Lights dim when A/C compressor kicks on


In the panel box, is the breaker for the condenser. Is it at the bottom, or the to p close to the main breaker?

Call your installer and ask them to check out the system. It could be over charged, and that can cause the compressor to draw a high amperage when starting.

A hard start kit has no ill effects on compressor start windings.
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Old 06-26-2011, 08:29 PM   #8
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Lights dim when A/C compressor kicks on


Yeah, but the compressor is on it's own circuit; so it there's enough AMPS per the spec on the motor, I don't see why the lights in the rest of the house should be dimming. Thanks.
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Old 06-26-2011, 08:35 PM   #9
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Lights dim when A/C compressor kicks on


Quote:
Originally Posted by beenthere View Post
In the panel box, is the breaker for the condenser. Is it at the bottom, or the to p close to the main breaker?

Call your installer and ask them to check out the system. It could be over charged, and that can cause the compressor to draw a high amperage when starting.

A hard start kit has no ill effects on compressor start windings.
The breaker for the compressor is at the very bottom of the panel. The electrician checked it all out, tightened everthing, etc..,
and said it's nothing in the breaker box or the wiring to/at the compressor.

I'll try to get the installer to come back too. Thanks.
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Old 06-26-2011, 08:46 PM   #10
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Lights dim when A/C compressor kicks on


I know its been said but its really a simple fix. You have high locked rotor amps, nothing abnormal. 80 percent of new units I see do. As far as it being bad for the comp windings that's just not true, it will actually extend the comp life. U will find that higher end systems actually come with hard starts and all systems show them as an optional accesory on the diagram. Definitely go with the 521 comp saver kit. Superboosts and other two wire hardstarts have a tendency to blow up.
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Old 06-26-2011, 08:54 PM   #11
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Lights dim when A/C compressor kicks on


have the breaker for the condenser relocated to the top near the main breaker.
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Old 06-26-2011, 09:22 PM   #12
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Lights dim when A/C compressor kicks on


Curious as to why?
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Old 06-26-2011, 09:26 PM   #13
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Lights dim when A/C compressor kicks on


Quote:
Originally Posted by quigleybmd View Post
Hi,
I just had a new central air system installed in my house. It’s a Heil system, with a 3 ton compressor. Whenever the compressor starts up, the lights in my house dim a little, very briefly. I had my electrician come back and look at it, and he checked all the connections for tightness, and the voltages and current. I have a fairly new 200AMP service. The voltage at the unit was consistently being 241-243 volts. It drops 2 volts at startup. He also measured the current at startup, and he measured 110AMPs. That’s quite a bit larger than the 77 AMPS written on the compressor label for ‘LRA’ (Locked Rotor Amps). with these very accurate electronic meters we have now they measure peak draw in milliseconds (and holds and records it) which may be misleading as it is for a millisecond and then normally drops and we did not have that accuracy or feature B4. He wasn’t sure if that could be causing the dimming or not (possibly a bad or weak startup capacitor?). He suggested having my installer call Heil to see if the 110AMPS is within spec. He also suggested having the power company check the taps and neutral connection at the pole. I would get that done and have them check the meter socket where the meter plugs in. They can get loose and cause problems and rural areas have more problems with unstable voltage/power than cities, at least where I am.

Has anyone else had a problem with lights dimming when an A/C system starts up? The electrician said it really shouldn’t be happening with my setup (new system, good 200AMP service, etc..). Any ideas or suggestions?

Thanks very much.

......
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Last edited by yuri; 06-26-2011 at 09:35 PM.
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