Lights Flicker upon NEW Furnace Start Up

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Old 11-22-06, 05:06 AM
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Lights Flicker upon NEW Furnace Start Up

This is my brother's house. It's had no issues prior to this. He just had a new geo-thermal furnace installed to replace his old geo-thermal furnace. The electrician that came in to wire up the new furnace said the current circuit would work for this new furnace and so wiring update at the box was required. You can tell when the furnace kicks on now, because the lights flicker (only at start up). There are two 200 amp mains in the basement and this geo-thermal furnace is wired to one of them on an 80 amp 220V circuit (The large amperage is only used for electrical heat back up..we've been told and there is another switch to over ride the electrical heat back up at the furnace..it's switched off when this flickering is occuring). I don't believe any of the light circuits on the other main box are affected; only the ones in the same box as the furnace. Any ideas? We've called both the electrician and the company that installed the new furnace; looks like their "experts" are off through the holidays. Thanks for your help!
John
 
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Old 11-22-06, 09:32 AM
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Is the new unit larger than the old one?

Some light dimming and flickering can be normal when HVAC equipment starts up because of the inrush current required to start the motors. Does the geothermal furnace have both a pump and an air handler? If so, you might see if you can set a delay between the start of the two motors. Usually furnaces will have jumper switches on the controller to program the delays.

Flickering can also be caused by a loose connection somewhere along the line. It can be anywhere between the appliance and the transformer out on the power company's pole. If you have the electrician back out, you could have him verify the connections to the subpanel and to the meter.
 

Last edited by ibpooks; 11-22-06 at 09:43 AM.
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Old 11-22-06, 09:48 AM
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Wink

Id say check the amp draw on start up. Could be that compressor in the new furnace needs a start kit. If you know electric You might go over all the wire tie ins and see that the screws are all tight on the wires.
 
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Old 11-25-06, 07:10 PM
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Thanks for the tips!
Yes, the new furnace is larger, but the current draw is lower on continuous running (by about 7amps) and higher on the start up draw (by about 7amps); according to the literature.
Yes, it has both a pump (actually 4 pumps) and an air handling system (squirrel cage fan). This delay feature you talked about, is it a built in feature of the current system and just needs to be set to activate the delay feature between the pumps and the fan motor so the draw doesn't occur at the same time? I'll be down to his house over the holidays and check it out; he's suppose to have the electrician back this coming week.

Thanks,
John
 
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Old 11-27-06, 10:42 AM
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> higher on the start up draw (by about 7amps)

That's almost certainly the problem.

> delay feature you talked about

I have no experience with geothermal furnaces, so I can only speculate. Most gas fired furnaces and A/C heat pumps have a jumper switch on the controller board that allows you to set a delay between the compressor start and the air handler start so that both motors aren't drawing startup current at the same time. Perhaps the geothermal furnace has a similar function.
 
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Old 11-27-06, 12:11 PM
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Wink

There are many time delays that you can get and use on the fan so it dont start with the pumps. By pumps I take it you mean a water pump the compressor and then the blower coil unit. You can get time delays so they can go in the 24V set up or in the 110V or 220V.
Not there cant see it. But Id set it up so the water pump comes on then the compressor and blower

ED
 
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