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Phantom Electrical Loads With Mitsubishi Minisplit

brettske | Posted in Green Building Techniques on

Hello everyone,

I recently finished building a pretty good house using a few single zone mitsubishi hyper heat minisplits. The 18K unit I mostly use will draw around 200 watts of electricity even when it is turned off. I don’t like paying for phantom electrical loads. I just noticed this this morning, and will start investigating why this is happening.

Could it be the hyperheat pan? I will see if I can disconnect that .

I also have 2 smaller 9K units that draw about 20-25 watts each when completely off.

Any tips or ideas would be appreciated!

Brett Greenburg
Moses Lake, WA

I have been a dedicated fan/follower of this site for 4-5 years and built my house using much of the advice here.

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  1. tommay | | #1

    If it is drawing power then it is not completely off. If it has a circuit board with electronic controls that tell it when to turn on and supposedly off, then it has to draw power. Only way out is to install a wall switch that turns the unit on only when you need it or use a timer switch.

  2. CollieGuy | | #2

    I was all set to purchase a Mitsubishi MUZ-FH12NAH until I discovered that the 130-watt pan heater runs continuously whenever temperatures fall below 0°C. The pan heater on the model that I ultimately chose only kicks on when the unit goes into defrost and shuts off when it resumes normal operation. This will reduce its energy requirements by several hundred kWh a year.

    Addendum: According to the Northeast Energy Efficiency Partnership entry for the MUZ-FH12NAH, the algorithm is described as follows:

    A) Heat mode is selected. B) The ambient temperature thermistor reads 32F or less for 5 minutes continuously. C) The defrost thermistor reads 30.2F or less for 5 minutes. D) Outdoor fan motor is turned ON.

    Apologies if I've misunderstood/mischaracterized its operation.

  3. this_page_left_blank | | #3

    According to the OEM supplied info, the pan heater should be 120W. It should also only be running when the pan sensor reads below 30.2F and when the outdoor fan is running. So it should be cycling when the fan is running, and not on at all when the fan isn't running. Still seems way too aggressive to me, but it definitely shouldn't be 200W continuous.

    My Fujitsu uses 3W when not actively heating. The defrosting of the pan follows some kind of algorithm that I haven't been able to identify yet.

  4. brettske | | #4

    Thanks for the reply Tom. I understand that controls can take some power, but .9 amps on 220v circuit seems excessive, especially compared to the .12 amps I see on the other 2 minis I have (9k units) when they are turned off.

    1. this_page_left_blank | | #5

      It is very excessive. Something is almost certainly wrong, and installing a switch will only mask the symptom (and only a small fraction of the time, as how often do you really want to completely turn off the automatically controlled heat?).

    2. Expert Member
      BILL WICHERS | | #6

      0.9 amps at 220v DOES NOT equal 198 watts on an AC circuit, at least not necessarily. Volts x amps = watts for DC. When working with AC power, the equation is volts x amps x (power factor) = watts. Most devices are something less than 1.0 power factor, usually less than 0.9 — and they are usually worse as power consumption decreases significantly.

      Want this means is you might be running really crummy 0.4 power factor in standby, which would mean that same “0.9 amps at 220 volts” is only around 79 watts. That’s still awfully high for power draw while the unit is “off”. I’d expect less than 10 watts, maybe a little more than that depending on how much of the unit’s brain is running while it’s waiting to do something.

      Note also that if you’re not using a true RMS meter, you’ll be introducing another source of errors that may be giving you a false idea of how much power you’re actually using here.


      1. Expert Member
        NICK KEENAN | | #8

        A resistive load -- such as a heating coil -- has a power factor of 1.

      2. this_page_left_blank | | #9


        I'm not sure that level of detail is needed for the discussion at hand. Based on his first post, I assumed he was using an energy monitor. I didn't picture him inserting a multimeter in series with the circuit. It's still not explicit how the measurements were taken, whether it was a power measurement with the amps extrapolated, or vice versa.

        "Most devices are something less than 1.0 power factor, usually less than 0.9 — and they are usually worse as power consumption decreases significantly."
        This is kind of assuming the extreme case. We don't know the source of the power draw, so we can only guess what kind of load it is. I think it's more reasonable to make a guess more in the middle of the typical range of PF, like 0.7.

        "Note also that if you’re not using a true RMS meter, you’ll be introducing another source of errors that may be giving you a false idea of how much power you’re actually using here."
        These errors will tend to cancel out the errors in power factor, as measurements deviating from true sine waves will read lower on an averaging meter. In some cases, this will actually dominate the error, meaning the actual power draw might be more than what is calculated, even in spite of a low power factor.

        Bottom line, if his heat pump is drawing 200W all the time, something's not right. If it's drawing 100W all the time, something's still not right.

    3. tommay | | #10

      Of course my reply was a bit of a joke, but how else do you remove all phantom loads. The first thing that should come to mind is, why is my heating unit outside or exposed to these cold temperatures? Makes one wonder.

  5. bfw577 | | #7

    Mini splits also have heated compressor belts that turn on to keep the compressor warm. They are necessary to cold start protect the compressor when you turn it on in extremely cold weather

  6. brettske | | #11

    So I was able to check inside the outside unit. Turns out it is the FH 18NA2 model and there is not even a pan heater! I was mistaken. My other units do have them. This makes the background draw even more surprising to me. There is a noticeable buzzing sound coming from the circuit board somewhere, and it is still drawing .9 amps when it is shut off. I am measuring the amp draw at the panel in the garage with a clamp ammeter. Power factor is new to me, and I'm not sure how that fits in with my RMS ammeter measurement and what the utility company measures and charges for.

    I'm going to contact my installer. Unit seems to work OK. This afternoon I had it running and keeping the room at a steady 72 with 36 degree temps outside. It measured 3.7 amps at the circuit while doing this. When I turned it off....back to .9 amps. Strange.

    Thanks everyone for you input and suggestions. I am open to criticism and learning new things.

    1. tommay | | #12

      Yeah, sounds strange. Buzzing sound, a stuck relay? Give it a whack. Or check the troubleshooting guide in your manual. View the check table lighting indicators, the mis-wiring checks and the test points for voltage to try to find the leak.

  7. walta100 | | #13

    It seems likely the load you are seeing is the heater inside the compressor. It is necessary because liquid refrigerant will migrate in the system to the coldest point and collect there.

    This is a problem when the coldest spot is the low pressure side of the compressor, should the compressor try to compress the uncompressible liquid it is likely to be damaged.

    It is not a phantom load if you intend on operating the system anytime in the next 12 hours, In fact it is necessary to insure proper operation of the system when it is cold outside. If you are not planning on operating the system for long periods of time you can turn off the circuit breaker so long as you to turn on the breaker 12 hours before you start up the compressor.


    1. cldlhd | | #16

      I was just curious as to where the turn the breaker on 12 hours before using the system comes from? this past weekend I connected a couple of CT clamps for my sense energy monitor and found out that my two Mitsubishi condensers are using between 60 and 70 watts regularly for up to 30 minutes at a clip basically every hour.... It's not that cold here in the suburbs of Philly, going down into the 40s overnight, but there's always a chance we might want to turn the heat on on a chilly day and 12 hours to wait seems pretty long. Is that only if it's significantly colder out?

  8. bfw577 | | #14

    Walter is correct. I have an electricity monitor on mine and can see my compressor heater come on. I attached a graph of that happening. The unit was turned off around 1640 and you can see the heater turn on at 1949.

    My 12k Gree Sapphire draws around 5 watts in standby and 30 watts with the compressor heater on. Seems crazy Mitsubishi would use a 200 watt heater. That is almost 5 kw a day and here in CT that would cost over a $1 a day just in standby cost.

  9. cldlhd | | #15

    My Mitsubishi mini split uses approximately 6W in standby but apparently it regularly pulls 60+ Watts regularly even when off. Not sure why. I know there's a pan heater but it was in the 60's yesterday and only went down to the 40's overnight

  10. joshdurston | | #17

    It's good that energy monitors are getting more mainstream, eventually I hope it gets to the point that it's embarrassing for a company to release a wasteful product knowing it will be scrutinized not just be regulators but by consumers. Right now I think they just hope people won't notice sometimes.
    Mini splits are a frustrating product for people that want to know everything about how something works. Much of the operating sequence is not publicly documented, and leaves people guessing and assuming.

  11. edwardmatthews | | #18

    Was there a resolution on this? Are these units working as intended with these high standby loads, or is there some configuration or installation error that can be fixed?

    I have a MXZ-3C24NAHZ2-U1 (hyperheat) that uses 0.95-1.09 amps constantly ($400-500 yearly at my rates!), apparently regardless of ambient temperature. I verified this with an energy monitor as well as a clamp ammeter.

    1. bfw577 | | #19

      It's your compressor crankcase heater and it can be turned off. Though I would highly recommend keeping it on due to the risk of severely damaging your compressor during cold start ups.

      From your models service manual.

      10-1. PRE-HEAT CONTROL
      If moisture gets into the refrigerant cycle, or when refrigerant is liquefied and collected in the compressor, it may interfere the start-up of the compressor.
      To improve start-up condition, the compressor is energized even while it is not operating. This is to generate heat at the winding.
      The compressor uses about 50 W when pre-heat control is turned ON. Pre-heat control is ON at initial setting.

      [How to deactivate pre-heat control]
      Turn OFF the power supply for the air conditioner before making the setting.
      Set the "4" of SW2 on the outdoor control P.C. board to ON to deactivate pre-heat control function.

      1. cldlhd | | #21

        I'm curious as to if there is a negative to changing this setting, especially during the winter months. I have taken to turning off my breaker when I know I'm not going to be using the heat or AC for an extended period of time. Right now I'm heating the whole house with my one living room / kitchen Mitsubishi mini split so the wall units for the bedroom I have switched off at the breaker

        1. edwardmatthews | | #24

          I found and other discussion that says pre-heat control was off by default in the past, so maybe it's not terrible?

          It seems a bit crazy to me to have an option that really will self-destruct the unit, but I'm not sure what the reality is. It's also strange that there's not a third slow-start / eco-friendly deep sleep mode that simply runs the heater long enough after new calls for heat (resulting in a slower initial thermostat response), rather than running it 24/7/365.

          I've also thought about turning everything off at the breaker during long periods of inactivity, but that feels a bit lame compared to the technical sophistication of the rest of the system.

          1. cldlhd | | #25

            I could see the idea of a slow start making sense. My breaker box is easy to access so I just figured it might be low tech but it'll work. As it gets colder I figure I'll just flip the breaker on and leave it run the way it wants to to protect the compressor. I have noticed that when it's warmer the standby usage stays down below 10 watts so apparently what others have said regarding this heating the compressor is accurate. I was a little surprised by it but overall I'm very happy with the units as I had oil heat before and this is much cheaper regardless. Also now that I know about this when I get those months in the spring and fall where I really don't use any air conditioning or heating I'll kill the breakers for both my outside units

      2. edwardmatthews | | #23

        Thanks, this is a helpful pointer. It seems like "pre-heat control" isn't the whole issue for me, as the manual says it should only be 50 W. At this point I would be happy to get down to "only" 50 W. I see alternating 30 minute blocks of 225 and 260 W all the time with the unit off, even when it's warm out.

        I believe the pan heater in my unit is 80 W, so even if it's (incorrectly) running continuously, I don't understand the usage I'm seeing. I'll reach out to my installer and Mitsubishi, but I'm also curious of any more tips from this community.

    2. cldlhd | | #22

      I have the same unit and that seems a bit high. When it gets down to around 40° f it'll pull about 60W for a half hour then down to around 5W for the other half hour continuously. When it gets warmer it only pulls around 5 to 10 Watts

  12. drewintoledo | | #20

    I’m interested to know if the Fujitsu units experience this same draw?

    1. CollieGuy | | #26

      I can't properly answer your question, but for what it's worth, our two Sanyo KHS1271 mini-splits draw 7 to 15-watts when idle, and anywhere from 35 to 40-watts when the crankcase heater kicks on (the service manual tells us its power draw is 20-watts). I'm not sure if it only operates when the outside temperature or that of the compressor falls below a designated set point as the service manual is silent on this. Typically, it remains off for fifteen minutes or so after I turn off the units, so it's most likely tied to the latter (note the behavior of the lines in the attached graph).

  13. HarryZaimis | | #27

    Hello Greg,

    I am a controls engineer at Mitsubishi. The answer is that your energy meter doesn't take into account the power factor, and is therefore giving you incorrect readings. In reality you are only drawing 3-15 watts when the unit is off; unless the compressor heater or pan heater is active, in which case you'd be drawing between 70-120 watts. All of these numbers are perfectly acceptable for any modern appliance, and especially for an HVAC system.

    Please let me know if you have any questions.

    1. edwardmatthews | | #28

      Thanks for the response Harry. Do you have any ideas for what's happening with my 3c24NAHZ2-U1?

      It uses 260 watts for 30 minutes, then 230 watts for 30 minutes, then repeats the cycle again, continuously. It does this no matter the outdoor temperature and even if we haven't run it for weeks or months.

      After a heat or AC call, it will drop to 0 watts for about 8 hours. After that, it returns to the 260/230 watt alternating pattern.

      This seems too high to be a power factor issue, and the continuous pattern makes me think it isn't the pan or compressor heater (unless something is broken and it's running those all the time?).

      Thanks for any ideas or troubleshooting suggestions you can share.

      1. HarryZaimis | | #29


        Actually it sounds like you're having the exact same issue as Greg, only that it's presenting itself in a different way.

        In the chart on page 2 of the following link, you can see that the base pan heater for MXZ-3C24NA models only draws 80 watts, and that it is only energized when the outdoor temperature is 39°F or less.\M_SUBMITTAL_MXZ-3C24NAHZ2_en.pdf

        In section 11-1 on page 81 of the following link, you can see that the compressor heater (labeled Pre-heat) only draws 50 watts, and although it isn't listed in this manual, it is only energized when the internal compressor temperature is 68°F or less.\MXZ-5C42NA_MXZ-2C20-3C24-3C30NAHZ(2)_SERVICE_OBH702H_11-20.pdf

        As you can see, the system is only capable of drawing a maximum of 130 watts when the units are not operating, and that's only when the outdoor temperature is 39°F or less. In other words, the 230/260 watt reading is due to your energy meter not taking into account the power factor.

        For future reference: no modern medium-large appliance draws 0 watts of standby power. If you ever see 0 watts, you can safely conclude that the meter is 'guesstimating', and probably isn't taking into account the power factor. There's a reason they're all marketed as "99% accurate" instead of "100% accurate".

        Feel free to let me know if you have any other questions.

        1. edwardmatthews | | #30

          Thanks Harry, this is very helpful!

          So assuming there's a power factor issue (or user error, as it's very suspicious that 260 is exactly twice 130, the maximum draw you noted!), what could explain the fact that it's hitting 130 W half the time every day, no matter the outside temperature?

          Is it possible that the 39°F and 68°F limits aren't working for my unit, since I see this usage pattern all through the summer?

          1. HarryZaimis | | #31


            Let me clarify - the 260 watt reading is completely false. Your energy meter isn't detecting the power factor, and is therefore giving you a reading of roughly 90x your actual usage. In reality you're drawing closer to 2.6 watts, not 260 watts.

  14. walta100 | | #32

    Power factor for a heating element seems unlikely generally heating elements are resistive loads having a zero power factor.

    Every energy monitor I have looked at did correct for power factor but I did not see what system Edward is using.

    Is there an ease way for Edward to understand what his temperatures sensors are reporting to the board?

    Since the wattage reading is double the likely accrual usage my guess is that the metering software is programmed for 2x the voltage applied or the wire is looped so it passing thru the sensor twice.


  15. this_page_left_blank | | #33

    Harry, both the loads you mention are resistive loads (compressor heater, pan heater). They both have power factors of 1. So your assertion that the 260W is erroneous due to the monitor not accounting for power factor is completely without basis in fact. On top of that, your assertion that the actual power draw is 2.6W, implying a power factor of 0.01 is pretty far out there. What device in the minisplit is operating at that power factor?

    Edward, what is the model of energy monitor you used? We can probably determine if it's measuring true or apparent power.

    1. edwardmatthews | | #35

      Thanks, I'm using a Uni-T B4Q094 true RMS clamp-on meter and an Emporia Vue (Gen 1) monitor. They both consistently read 1.1 A on one leg of the 240V circuit during the high usage times.

      I'm super curious about this and always like an excuse to get a new tool, so I ordered an Amprobe ACD-51NAV power quality meter that should actually measure the power factor. I also plan to shut off all circuits in the house except for this one for an hour or two and check the main meter usage, but I haven't run that experiment yet.

      My hypothesis is still that the ambient air thermistor is bad, since I don't see any changes in reported usage as the outdoor temperature changes (as discussed above, it should vary at 39°F and 68°F). It seems unlikely that the power factor is changing to exactly cancel out the effect of the pan heater coming on, even if the absolute numbers from the energy monitor are wrong.

      1. cldlhd | | #37

        I subscribe to that theory 100%- every new project is an excuse to buy a new tool(s). I think click and clack on Cartalk laid it out in detail years ago, maybe even had a name for it

  16. Expert Member
    BILL WICHERS | | #34

    My guess is the "energy meter" in use here is actually just responding to an average, and not a very good one at that. Most good energy meters that read watts take many (hundreds or thousands) of samples of both voltage and current simultaneously, then sum them over a period of time to arrive at a wattage value. If a voltage average and current average are used instead of a stream of simultaneous samples, you lose the phasing information, which makes your results meaningless. Similar error happens with non-RMS volt meters.

    All power factor is is the ratio of watts to volt*amps. A power factor of 1 means volt*amps and watts are the same, and you can just measure voltage and current and multiple them together to get watts. This works with purely resistive loads like electric resistance heaters, but not for any complex circuits which include motors and almost anything that rectifies the AC into DC. A power factor of 0.5 would mean wattage is ONE HALF of the sum of volts and amps. Some things will introduce additional error in the case of leading power factor (as opposed to lagging power factor too), which is the case with heavy capacitive loads.

    The short answer here is that your E meter is probably not a particularly accurate one, and you can't trust the results.


  17. brad_rh | | #36

    Another possibility is that the HP may only use one leg of the 220 for the heaters, so it's only 110V, and the load is 130W instead of 260W

    1. joshdurston | | #38

      Good point, you verify this you could try moving the current transformer to the other leg of 240V and see if the readings change. Ideally you would measure each leg independently if the loads are mixed 120/240v rather than one 240v load.

    2. this_page_left_blank | | #39

      This is highly unlikely. I have two miniplits, and neither of them even have a neutral connection, meaning only 240V is available. I'd be surprised if any minisplit was any different.

  18. edwardmatthews | | #40

    With better measurement technology, it looks like the "issue" with my system is just low power factors (and Harry was basically right above, sorry for doubting you!).

    I used an Amprobe ACD-51NAV power quality meter and cheapo $20 power meter from Amazon (highly recommended) that both measure true power and power factor.

    In alternating 30 minute windows, the compressor pre-heat comes on with power factor 0.20-0.25 (true power usage ~50-65W). It's about 1.1A, which led to my previous confusion about high power usage.

    When pre-heat cycles off, the power factor drops to 0.01-0.02 (!) (true power usage 5W or less). This part of the cycle shows 0.95A, which again contributed to the confusion with my earlier meters.

    I will probably end up turning off pre-heat since we rarely use this system for heating, but now I'm better educated and equipped to track power usage through the summer.

    1. this_page_left_blank | | #41

      I have to eat my words as well. I never would have imagined that the power factor would drop as low as 0.01.

      Now we know that Emporia Vue is a junk energy monitor. I seem to recall that model being suggested in this forum before.

      1. Expert Member
        BILL WICHERS | | #42

        Power factor for very light loads can sometimes be really bad, especially with certain types of power supplies. It doesn't matter much though, since the increased system losses are still small since the overall load is still very small. My guess is that the minisplit has a power factor corrected power supply only for the larger loads, but the small standby supply probably doesn't. It's possible that the additional system losses from the power factor correction circuitry (which is usually implemented as a chopper ahead of the main power supply in the case of switching power supplies) may introduce more losses than the very small load does with no correction at all. Design tradeoffs are sometimes counterintuitive in that way.

        A suspect many of the cheap energy meters have very poor accuracy with both very small loads and larger loads with poor power factor. It's far easier to implement a simple "volts x amps" function in a meter than it is to do the proper watt measurement using lots of simultaneous volt and amp samples over the waveform.

        An oscilloscope with a current probe would be a good way to check for goofy metering issues like this.


  19. cldlhd | | #43

    That's good to see. I know this is an old thread but my sense energy meter normally learns and guesses what a thing is but for the mini splits I attached the optional CT clamps on the individual circuits because they are the ones I was most interested in regarding accuracy. My energy meter was saying last night that my outside MXZ-3C24NAHZ2-U1, for my bedrooms is continuously pulling around 65 Watts for a half hour then 11 for the next half hour back and forth continuously. It's been going down around 45° at night but going up into the high 60s early 70s and the day so I just killed the breaker for this week. I figure I'll take Walter's advice and turn it on at least 12 hours before I start using the heat.. interestingly, or not, my outdoor unit I have for my general living space-a Mitsubishi muz-FH15NA uses the same approximately 65 w for 20 minutes then drops to zero for 50 minutes back and forth continuously...

  20. elizilla | | #44

    Hello, apologies for resurrecting an old thread, but I have the same ongoing draw with my Mitsubishi mini split system. It is winter, I live in the frozen north, and I only use the mini split for air conditioning. And you guys say it is just doing this to protect the compressor from starting with the coolant too cold. Since I don’t heat with mini splits, it is definitely safe to just turn off the breaker until the first hot day next summer, right?

    60 watts running half the time over the course of a month, is like 20 kWh per month. That’s a savings worth the trouble!

    1. cldlhd | | #45

      First of all, I'm not an expert but Walter seemed to say that it shouldn't hurt it to shut the breaker off If you're not using it as long as if you plan on running it for heat, you turn the breaker back on at least 12 hours before starting the inside unit. I have the same 65 watt usage, I have two outside units when it's not that cold. I run my one mini split and the main area for heat and if I know I'm not going to use the bedroom units, which are attached to the other outside compressor, I will shut its breaker off. I've done this a few times and just make sure I flip the breaker on a while before I start the unit. I haven't had any issues

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