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A few months ago we had our gas furnace replaced with an air source heat pump, using our existing ducts in our single level 3 bedroom house. As part of this update our electrical service was upgraded from 100 to 200 amps, and the panel was replaced with a new one. The heat pump is on its own dedicated circuit running from our panel to a junction box outside next to the heat pump.

Since this update, whenever the heat pump is running and either cooling or heating, most of the dimmable lights in our house flicker the entire time the heat pump is running, not just when it starts up. The flickering is VERY pronounced, not a quick blip but more like a haunted house.

Almost all of our lights are dimmable and all are LEDs. I understand there are lots of compatibility issues with LEDs and certain dimmers, but this issue impacts so many different types of lights and switches that it seems to be an issue with our electrical service or the way the heat pump is wired in. The flickering wasn't present before, with our old panel and 100 amp service – certain lights would occasionally flicker a bit at certain dim levels, but not constantly like they do now.

The bulbs we are using were made by a wide variety of manufacturers (at least 7 different manufacturers), a mix of cheap and expensive bulbs in lamps, par20 cans, and LED lighting fixtures, using Lutron Caseta, Leviton sliding dimmers, Ikea lamps with built-in dimmers, etc. The bulbs were all sold as dimmable, and marked as dimmable on the bulb.

Our HVAC contractor has been back about 6-8 times to try to identify and fix the issue with the flickering lights, with no luck so far. On a recent visit they brought some replacement bulbs and seemed to think we should simply replace the bulbs that are flickering, but I don't want to do that since it impacts most of the lighting in our house and I don't want to have to live with this nuisance for the next 20 years. Also it seems like a flaky power supply might not be good for our other electronics. (computers, a/v)

What can I do to identify and diagnose this issue, and prove that it's an issue beyond the symptom of flickering light bulbs? I have a multimeter but don't have much experience with it; can I use it to measure the voltage drop on the other circuits in our house when the heat pump is running? Is it normal for the voltage to drop and stay down or fluctuate the entire time the heat pump is running, or just when it first ramps up? Is a voltage drop the thing I should be looking for, or is there something else I should try to measure as well?

Our HVAC contractor has been taking responsibility for this issue so far but after spending maybe 30 hours of staff time on it and running out of things to try I'm worried they might just blame it on our bulbs and give up. I'd like to be able to present them with evidence that something's wrong, aside from the flickering bulbs.

Our power company has also come by to confirm the supply wiring is OK, and replaced a badly corroded neutral connection but that didn't help either. The original wiring in our house is about 30 years old and we replaced almost all of the lighting and switches about 5 years ago.

Edit: important detail I neglected to include: the HVAC company were the ones who did the electrical service upgrade and all the related wiring. They also added a 'flicker free breaker' from Siemens on the heat pump circuit to try to remedy the flickering.

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  • I don't have much time right now and will think about this later, but have you tried putting at least one incandescent bulb on the same circuits? They tend to even out the fluctuations from the dimmer, also, you might need a better dimmer switch. Do they flicker when the dimmer is turned up all the way? Nov 18, 2022 at 2:45
  • @GeorgeAnderson I will try with an incandescent bulb, if I can find one. This issue is present with at least 5 different types of dimmer switches: Lutron Caseta hardwired in-wall switches, Lutron Caseta lamp modules, Ikea desktop lamps with built-in dimmers, Leviton in-wall sliding dimmers, Ikea Dimma dimming cable on a standing lamp, and maybe a few more. They do not flicker when turned up all the way.
    – gosko
    Nov 18, 2022 at 3:41
  • What size is the heat pump circuit? Make and model? Nov 18, 2022 at 4:01
  • @manassehkatz-Moving2Codidact The heat pump circuit is 50 amps. It's a 3-ton system made by Moovair, model numbers DMA36HOS20230E7 (outdoor) / FMA36HIAHUU230X7 (indoor)
    – gosko
    Nov 18, 2022 at 5:09
  • A quick look the specs and it looks like a reasonable system, assuming it is sized appropriately for your house. (But if it is too large or too small that will affect comfort and energy usage, should not affect dimming LEDs.). That being said, I have to wonder if somehow the inverter compressor is at fault. Doesn't make sense, but that is likely the biggest change compared to previous air conditioner. (and it runs both heat and cool) Have you talked to Moovair? Nov 18, 2022 at 5:33

5 Answers 5

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The HVAC company brought you bulbs because they want you to go away. That's fine; unless they are the ones who did the service upgrade, this probably isn't their responsibility. It's more likely that you still have a poor neutral connection or some other significant electrical installation problem. However it is also possible that the heat pump is defective in a way that is causing all sorts of noise across your system. You won't be able to spot that with a multimeter.

If I were in your spot, I would be calling around local electricians looking for one who could do power quality analysis at my house. This will probably cost you a significant amount of money, but it's the only way you are really going to nail down what is causing this flicker. They should be able to show up with a power quality analyzer. You could rent one, but without the experience to use it you'll not know what to do with any data that you gather. You need someone with significant electrical troubleshooting experience to really dig in here.

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  • Very helpful, thanks. The HVAC company did do the service upgrade.
    – gosko
    Nov 18, 2022 at 5:04
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An HVAC company doing an electrical service upgrade? Get a licensed electrician in there and have them give the system a once-over. There are many things to mess up, and HVAC outfits are notorious for playing fast and loose with Code.

First, get some real incandescents and replace some of the LEDs. No not permanently, just for testing. "Looks like an incandescent but is actually a halogen inside" are close enough. Incandescents are truth tellers because they remove all the LED weirdness especially the "train full of dumpsters that was on fire before it derailed" that is the state of the art of screw-in LED dimming. If you have a group of lights under control of one switch, replace exactly one of them with incandescent and see if that makes the LEDs behave. Does a room full of incandescents also shimmer? Then we can distinguish a real power problem from LED nonsense.

I'm not an LED hater. Lots of dimming technologies work great with LED, like 0-10V, PWM or powerline coding. But those are not compatible with screw-in Edison bases.

You should probably buy a Kill-A-Watt home energy monitor. It's cheap. It's a safe and foolproof way to get voltage readouts without sticking probes in slots (what could go wrong lol). You can also plug in a pure resistance heater like a space heater or toaster and compare the "watts" (the power actually used) and "VA" (the sine-wave that must be delivered to serve that power). On a resistive load they should be identical. If they're not, your power isn't a sine wave!

You should also hit the books on North America's split-phase power system and how panels are phased. That way you will be able to monitor both "legs" of power separately.

My hunch is they may have done something dumb with neutral or grounding, and created a Lost Neutral scenario in which your voltages float around (or rattle when an inverter drive is nearby). Lost Neutral is a hard one to detect because stuff "works" by and large.

Other than that, this sounds like some sort of a bodge, like miswiring or failing to upgrade the service conductors when doing a 200A heavy-up. There are too many possibilities to name, really.

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    "Looks like an incandescent but is actually a halogen inside" are close enough. is because halogens are incandescent. They work the same: by getting a filament hot, just a bit hotter with the gas mix in a halogen bulb
    – Chris H
    Nov 18, 2022 at 11:39
  • The HVAC company I used for my last heat pump had an electrician on staff who did the electrical part of the work. This could be the case with bigger companies.
    – KMJ
    Nov 18, 2022 at 15:52
  • @KMJ yes, but they often do that work very absentee, delegating essentially all the electrical work to non-qualified personnel. Code allows supervision, but not from such a distance! Result: atrocious work. On another forum we have a guy who's been struggling for a month to get solar signed off by the inspector, because the electrician who is approving drawings has never seen the site and violently insists things are correct, which they would be if field conditions matched the drawing. Nov 18, 2022 at 21:30
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    Fair. The electrician doing the work was great, maybe that was an outlier.
    – KMJ
    Nov 18, 2022 at 21:31
  • @KMJ yeah, it's also the Great Resignation x the Building Boom. Too few electricians spread across too many jobs. Nov 18, 2022 at 21:41
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We have also been having the same issue with led bulbs while our heat pump is running but we do not have any dimmers. Anywhere we have an led bulb, we have a constant flicker, or the bulbs will dim while the heat pump is running. In 2 different rooms we have an issue where if the heat pump is running and the lights are turned on, one bulb will not light, or will come on dim once is does come on. If the lights were on before the heat pump kicked on then they will operate normally but may flicker a bit.

I myself checked everything out myself including the heat pump, no voltage drops, no loose connections anywhere, and if i found anything suspect I tightened it or replaced. Finally I threw in the towel. We had an electrician come out and verify everything in the house is fine. He replaced the heat pump breaker but that did not change anything.

We had an hvac tech come out and speak with Bosch (the heat pump manufacture) and the support tech said they just had a class on this that they have had complaints with variable speed compressors causing led lights to flicker. He had the hvac guy run some tests on the compressor and said it is operating normally and that the only answer is to try some new bulbs. It does not cause issues with incandescent lights. I swapped some old bulbs in areas we have noticed the issues and voila no flicker. Problem is you cant find them anymore, except on rare occasions in small quantities and they are now more expensive then name brand leds.

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    Somewhere, buried in that wall of text, seems to be an answer. Please take a few moments to edit your answer to make it easier to read. Also, "voilà", not "walha". ;)
    – FreeMan
    Feb 28, 2023 at 14:20
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    Yes, switching to incandescents resolves the issue but I'm not doing that.
    – gosko
    Mar 2, 2023 at 23:06
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    I suppose that, technically, "swap an incandescent in for an LED" is a solution to the problem, but it's not a practical one for a number of reasons, including the fact that incandescents are an endangered species. I'm not sure that this really answers the question by Home Improvement standards...
    – FreeMan
    Mar 31, 2023 at 12:50
  • Is there any known way to guarantee the quality of power on a lighting circuit even when one of these appliances are running on a separate circuit? We have this problem as well. Oct 6, 2023 at 1:02
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Moovair, Bosch, and many other manufacturers are all a Midea unit re-branded. I can confirm Midea made a design change to one of the boards on some of their heat-pumps (3t and 4t) to address this exact issue. The contractor should be able to replace the "Inverter" board under warranty, which in many cases (assuming it is not a wiring/panel issue) will solve the flickering.

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  • There were no brand names specified in the question for the heat pump. What makes you think that it's one of the ones you've mentioned?
    – FreeMan
    Feb 1 at 16:44
  • OP gave the Make/Model: The heat pump circuit is 50 amps. It's a 3-ton system made by Moovair, model numbers DMA36HOS20230E7 (outdoor) / FMA36HIAHUU230X7 (indoor) – gosko Nov 18, 2022 at 5:09
    – Ryan.
    Feb 1 at 16:56
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    and... that's what happens when useful info is buried in comments instead of added to the question... mea culpa
    – FreeMan
    Feb 1 at 17:10
  • Thanks, that's very helpful info. Do you know when that design change was made, and if there is any public info available about it? I already had the control board replaced once, in July 2023, after the manufacturer indicated there was an updated board available. That update was intended to address some issues with the thermostat not maintaining the set temperature properly. But maybe the control board is different than the inverter board.
    – gosko
    Feb 2 at 18:21
  • Depending on the manuf, maybe 6-8 months ago? It would not be the same board that was updated to address temp control issues. No public info, this would have been communicated to contractors through distribution channels.
    – Ryan.
    Feb 5 at 16:55
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Try a higher end lamp like Phillips dimmable. These have worked for me in the past for similar issues.

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