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Community and Q&A

Disappointing phantom load on 27.2 SEER Fujitsu 9RLS2 minisplit

user-939142 | Posted in Energy Efficiency and Durability on

Looking for anyone with measurements of their mini-splits phantom and idle wattage use.

My newly installed 9RLS2 is using 80 watts, both when off and on but not running.
Other measurements while operating have been in spec range and are fairly impressive.

So I take it that SEER and HSPF ratings must not effectively measure/include phantom or idle loads. Heck just the fan at full speed uses only 25 watts

Kinda disappointed this thing will suck 2Kwh a day when not in use or during half days say when it only runs part of the day (night cold or noon heat) which hitting the breaker to kill the unit completely is not user friendly. On those days with little heat need, that 2Kwh could better go to a old inefficient resistance heater.

It feels like this is an oversight somehow.

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  1. Expert Member
    Dana Dorsett | | #1

    High standby loads of mini-splits are a well known issue, which is why sizing them correctly is important. Oversizing them to where they're cycling rather than modulating at low duty-cycle cuts severely into net efficiency.

    During periods of very low load it's fine to simply turn them off (with a power switch, not the remote.)

  2. jinmtvt | | #2

    Bob, i've just installed 4 of those ( newer H model ) in my house, but i have no mean
    to measure electricity usage ... what are you using to monitor ??

    how do you like the abscense of noise from the exterior unit ?? :)

    i have not read any "standby" power usage in any of the doc, will look through
    service manuals tonight if required..

  3. jinmtvt | | #3

    Dana : i don't think installing a 240V switch or a remote contactor and having to switch is off is worth it for 7$ or less ( the standby doesn't count when it is running ) per year ... probably more in the 2-4$ worth...

    still ..wonder why 80w ...

    also, the 9K btu is pretty much the most efficient and the smallest available.

  4. user-939142 | | #4

    You've lost me Dana

    As this is the smallest model, over sizing would be tough.
    And while trying to size so a unit is always running at low duty may mask the 80 watt load, it is a bit unrealistic in many climates where the weather does change or in buffer seasons where only peak/low noon and nigh time temperatures require some heating/cooling.

    Is it common for people to install a hard 'power switch in the home for these things, outside of the fuse box or outside disconnect? Feels not very practical.

  5. Expert Member
    Dana Dorsett | | #5

    Bob- I'm not saying that there's anything YOU can do about it being oversized for the shoulder season load other than a hard power-switch, but pointing out one of the hazards encountered when people do dumb rule-of thumb sizing and end up with a 2-ton mini-split for a 5000BTU/hr peak load, and the thing spends it's whole life in standby mode.

    The reason for the high standby loss is that the power supplies and are all up & running to keep the control boards (basically embedded computers) on alert 24 hours/day waiting for the call to do something. In most cold-weather units there are even resistance heaters keeping compressor bearings & components at a temp where they will always be within mechanical tolerance so that it can start up without damage, but at least those usually automatically turn off at higher outdoor temps. (Wintertime standby losses can be a couple hundred watts.)

    The highest efficiencies tend to occur at the lowest speed, so there's no "masking" of the load of the control power use- it's fully integrated into the SEER/HSPF numbers, since the power to the controls is not separate from the rest. As long as the compressor and blowers are turning (even at min-speed), it's still moving heat. When it's all just idling, it's not.

    I'm not sure how many people bother to install hard switches, but those who care about standby losses can kill it at the breaker. But if you need the thing to be able to respond to the remote at your whim, the power to the controls need to be booted up and alive, and for your version of the 9RLS2, that's apparently 80 watts. I suspect that even within a model name the standby losses have been incrementally falling with design revisions to the sub assemblies, but I don't really know that. The engineering teams behind these beasts are well aware of the issue, but there's a stronger drive for enhancing the operating efficiencies to get higher test numbers than there is to reduce the standby losses. Like desktop computers, it clearly IS possible to design "sleep" modes to the controls down a more power-sipping level, but the market hasn't really demanded that (yet.) I fully agree that 80W of phantom load per unit is pretty power-piggy (and why multi-splits are sometimes a better solution than 3-4 single units, despite lower SEER/HSPF test numbers.)

    Jin- why four? Can you turn at least some of them off on a seasonal basis, let the others carry the shoulder season loads?

  6. user-939142 | | #6

    I found an online blog where the writer mentioned the prior model 9RLS consuming 60 watts.

    @Jin: Yes the near silent outdoor noise is pretty impressive.

    I'm measuring using an Effergy clamp on unit, similar to a TED and the like.
    It is an inexpensive unit that is portable, which I like as I can use it to test/check usage, and it's wireless unlike the TED. I don't really need to spend 10 times as much or log every appliance separately 24/7.

    You can also make your own modified extension cord, so you can measure small items at the outlet instead of at the panel.

    If you want to check your units. Try to get your home to a stable load, where your meter is consistent - even better if you can get nearly everything off. Then measure the meter with the units on and off at the breaker. A 320watt change will be easy to measure. make sure the remotes don't trigger the units on; also possible the systems may draw a bit of power when you flick the breaker on.

    google: reading your meter, pretty simple. i used it to fact check that my effergy was correct within its range of error.

  7. user-1135248 | | #7

    My Daikin exhibits the exact same 80 - 100W standby load and
    the resultant 2 kwh/day or so consumption. The bulk of it goes
    to the compressor crankcase heat, which in this case [and
    probably most other modern units] is done not by resistance
    heating, but by the inverter itself bleeding a little extra
    current through the motor coils in a way that creates heat
    but doesn't actually turn the motor. And when it does this
    is intermittent, so I don't see the current draw all the time.

    If I listen very carefully at the outdoor unit I can hear a
    high-pitched whining from the electronics when it's doing
    this warming stuff, and nothing when it's not. I also have IR
    shots in my house-saga clearly showing that area of the condenser
    unit staying warm [which is one of the things that tends to
    attract critters into them in cold weather, so screen off all
    those holes!]

    Ironically, the system still does this in the height of
    summer when no compressor heating at all is needed to keep
    the oil properly fluid. You'd think they could check the
    outdoor-ambient temp sensor mounted RIGHT THERE on the back
    of the unit to decide whether to bother with warming or not.
    At least the compressor is all wrapped up in a thick blankie
    and doesn't lose all that heat quite as fast...


  8. jinmtvt | | #8

    Dana : i got 4 because of the distribution problem house is 60ft long open space on the first floor
    so instead of getting 2 heads i got 2 full units ( almos same price, higher efficiency , shorter hose lengths )
    the second floor is still 60ft long, and only has a 45ft corridor linking everything together
    ( 3 bedrooms and 1 bathroom ) so we installed one unit on one end of the corridor and at the other hand, in our master bed room

    still have to finish the 4th ( 2nd floor corridor one ) but up to now they've worked perfect in the few 30c days we had , even though i have yet to install some large sunshades outside, and i still haven't fixed window issue.

    Neway i'm pretty sure they will pay for themselves within only a few years because of the heating efficiency ( currently was 100% electrical underfloor heating )

    Vive les pompes a chaleur!! :)

  9. user-939142 | | #9

    I'm measuring a solid 80 watts continuous, although I guess all systems employ a bit of different logic, or not much at all it seems.

    So I'm guessing the HSPF and SEER/EER ratings models don't quite capture this standby and/or phantom load otherwise it would be optimized.
    As noted, using the thermostat to limit the crankcase heating when the temperature is high or the unit is turned off would make sense and be free.

    Just surprised no one using these units in high efficiency homes has noted this before in reviews. The 80 watts nearly doubles my homes phantom load, and is 5 TIMES HIGHER than my old inefficient Trane whole house system.
    An article on this site noted a garage door opener having a whopper 20 watts phantom load, which makes this seem ridiculous.

  10. jinmtvt | | #10

    5 times 0 = 0

    are we still discussing a ~3-4$ yearly load ??

  11. GBA Editor
    Martin Holladay | | #11

    80 watts continuous is about $87 per year. You can subtract out the percentage of time when the minisplit is actually heating and cooling -- that will lower the annual phantom load.

  12. jinmtvt | | #12

    Martin: wow can a single digit make a difference :p
    i ended up with 7-8$/year ... thus divided in half to remove running time of the splits :p

    40$ is not much, but its now reasonable to discuss about it !
    ( even more if you have 4 minis as i do :p )

  13. gusfhb | | #13

    I installed double pole switches on the first two units I put in, since it appeared the wiring diagram called for them. An actual electrician installed the later ones and no switches. IIRC the 30 amp double pole switch, box and plate would pay for itself with in a year, if you remembered to use it. I never did because i never thought about the standby load.........

  14. user-939142 | | #14

    Did you install the switches leading to the indoor unit?
    That is what most diagrams I've seen called for (Fuj, LG, Sam) although they call for 3 pole. It appears that is an electrical code / safety issue, and it would Not affect the phantom load issue as that is out at the outdoor unit. It is not code here, and those 3 pole switches are pricey so I skipped it.

    I have a disconnect at the outdoor unit, also code. And a fused connection at the breaker. Neither are convenient. I did splurge for the GFCI breaker.

    I agree that putting an on/off switch near the unit would help, varying on how your local weather is and how interactive you want to be. On would hope the on/off switch on the remote would accomplish the same thing, doh!

  15. gusfhb | | #15

    Installed as per the wiring diagram, Suppose you could pull the disconnect if it did not work.[edit or switch the breaker] The third wire is just signal, I do not recall if the mitsu showed a 3 pole, I used a double pole and left the signal connected

    [or switch

  16. jinmtvt | | #16

    Do you guys have a long period that doesn't require cooling or heating in your climate ??

    I don't think it would be very usefull in my situation ( QC ) i can't think of much more than 2 months
    on and off depending on extremes we get during spring time.

  17. user-939142 | | #17

    @Keith: That in between disconnect wouldn't help as it doesn't turn off the outdoor unit. It's possible on some models the outdoor unit would see that as a fault and switch some things off, but with it in the spec, that is doubtful.
    I clamped the meter on the feed running to the indoor unit and it basically showed no usage when off (varied within the error range of the meter)

    @Jin There are three types of periods this would affect.
    1. The dormant seasons when you don't need HVAC at all. biggest losses here
    2. The peaking seasons when you don't use the HVAC much at all, especially if your home is designed well, but you need heat on late cold nights, or cooling on hot afternoons. nearly the same amount as loss as above, excluding the 2 hours of use a day.
    3. Heating/Cooling Seasons with frequent use, losing a little juice while not running, yet adding back in some heating efficiency during the heating season.

  18. curtkinder | | #18


    And to think I've been known to whine about the standby loss of a conventional split heat pump system! In the case of my own it runs about 22 Watts in cool mode and 12 Watts in heat mode. The extra 10 Watts, I surmise, arises from extra control power consumed holding the reversing valve in cool mode. I've looked into providing the required 24 VAC control power via more efficient means in order to combat what I believe to be excessive standby usage. The typical control power transformer, energized 24/7/365, is almost too hot to touch, a veritable dinosaur in this age of switching power supplies.

    Considering this issue from another angle, my 3500 SF Florida home is heated and cooled using about 3000 kWh annually. While I grant that it has a pretty good envelope and a nifty water source heat pump, I have reason (consumption data) to believe it would do almost as well using a Trane 20i or Carrier Greenspeed, two high end air source heat pumps.

    While I am (now make that "WAS") as enamored of minisplits as the next energy geek, it looks as though if I chose to condition a similar home with several individual minisplits, the phantom / standby usage of 3-4 minisplits could approach the TOTAL usage of a premium conventional split system. That is both amazing and totally unacceptable!

    This topic deserves, at minimum, its own blog post and much deeper investigation into the standby load of various minisplits in order to reveal differences between brands and highlight those that perform better than the abysmal usage reported here.

  19. GBA Editor
    Martin Holladay | | #19

    I just sent an e-mail to Marc Rosenbaum (who has a Fujitsu minsiplit) to ask him what he knows about his unit's phantom load. He responded, "Mike Duclos has data on this, and some info about how the power factor is really bad when the unit is in standby, so that the apparent W aren't the true W. My system didn't show this level of usage as far as I know - I have a old style glass-front [kilowatt-hour] meter on it, and when it is turned off at the remote control the disk doesn't spin. My experience is that usually loads of 30W or more make the disk spin - 80W would be a lot of power for the utility to give up. This past winter, more normal than the first winter I have full data on, my house used 1,462 kWh for heat over a 6 month period. How much is standby I don't know."

    I have left a message with Mike Duclos to learn more; I'll report back if I have more info to share.

  20. GBA Editor
    Martin Holladay | | #20

    A follow-up e-mail from Marc Rosenbaum: "By the way, I have quite a number of days when the meter [connected to the Fujitsu minisplit] read zero additional kWh over the previous 24 hours. This of course could be that the meter can't read low watts, but 80W continuous is 2 kWh/day."

  21. GBA Editor
    Martin Holladay | | #21

    I just spoke with Jason Cruze on the technical help line at Fujitsu. He said that the maximum phantom load for the Fujitsu 9RLS2 is 0.1 amp. At 240 volts, that's 24 watts. If anyone is measuring 80 watts, Cruze recommended calling a technician to find out what's wrong with the unit.

    He said that there is no heater or freeze protection on the 9RLS2. (However, there is a heater on the Fujitsu 15RLS2H, so one would expect the phantom load of that unit to be higher in cold weather.)

  22. GBA Editor
    Martin Holladay | | #22

    I just received an e-mail from Mike Duclos. Mike wrote, "I’m not sure about which model the 80 watt phantom load was measured on (I haven’t looked at the thread), but I’d suspect measurement technique.

    "I ran into this with the first generation eMonitor at the Montague PowerHouse, which has a Fujitsu 9RLQ – when I first hooked up the eMonitor, I saw [a phantom load of] 90 watts plus continuous.

    "Long story short, I contacted Bill Hick, Fujitsu NE sales manager, who quickly referred me to someone from Fujitsu on the west coast who had already been through this with another eMonitor user.

    "Power House Dynamics, maker of the eMonitor, had an issue with their power factor correction circuit which they subsequently fixed, and retrofitted to old units (including mine) N/C.

    "Following that, I was seeing very low power (near zero, measurement accuracy at very low power levels may have been a factor) up to about 20 watts intermittently during standby. ...

    "If the people doing the measurement don’t understand about power factor, that could easily be the problem.

    "FYI, Power House Dynamics has been incredibly supportive when I’ve had eMonitor power factor questions (you may recall the infamous induction cooktop), even lending me a pricey power factor meter for some measurements that confirmed what I had documented with an oscilloscope.

    "I hope this is helpful."

  23. Expert Member
    Dana Dorsett | | #23

    An intermittent 20 watts during warm-weather standby is certainly getting toward "reasonable", but probably still points toward using multi-splits rather than multiple mini-splits where possible, especially with the cold-weather units with heaters. It would be nice if the standby power numbers (across temperature, where applicable) were included on the short-form specs from manufactureres.

    Thanks for chasing that down!

  24. jinmtvt | | #24

    Dana: if it is intermittent it could be anything ... 20W is not much though

    Can't wait to read more about this as i've just completed my 4th 9rLS2H installation :p

  25. gusfhb | | #25

    RE: Dana

    I think the difference in performance between the mulitsplits and the best available single units would more than make up the difference.

    We don't currently use the minisplits for heat but our heat ran [sporadically] till early June. Had AC on as early as mid June, and it will run on and off until early September and the heat will be on in mid September.

    In my climate it probably makes sense to turn them off at the breaker if using ac only

  26. user-939142 | | #26

    Thank you Martin for the research.
    One of my hopes was to get some official feedback as I know I would get nothing useful contacting Fujitsu. I knew the PF could be low as it was listed in one of their specs, but it didn't specify when that PF occurred in usage.

    So to test, I disconnected everything at the breaker panel except the mini split on its own circuit. First I checked with the circuit off, the outside meter didn't move at all over 5 minutes.
    I then turned the breaker on for the mini-split and got a little bit of movement. After about 10 minutes the meter stopped moving again, so the actual power usage is intermittent at least in the summer while the unit is off.
    This would be roughly 10 watts.
    The clamped on power meter continued to report 80 watts even while the meter wasn't moving.

    I'm going to try and put my multimeter on that circuit and see what i can measure at phantom and idle loads. I can't leave the whole house in the dark for long enough to monitor usage at the meter, especially in this heat.

  27. user-939142 | | #27

    Does the voltage the mini-split accepts/consumes on the main circuit stay at a consistent value?? I can't measure both voltage and amperage at the same time with the multimeter, but I assume the voltage is consistent to calculate the wattage.

  28. curtkinder | | #28

    Consider a TED energy monitoring system to track down the loads. I've found TED to be quite accurate, down to just a few Watts, and it incorporates power factor. TED is a bit flaky, in my experience, relying on AC wiring to transmit consumption data, which is vulnerable to noise introduced by ubiquitous switching power supplies.

  29. user-939142 | | #29

    I've got a PF corrected measuring meter on the way. The Efergy folks have been very helpful and easy to work with, offering a free exchange.

    The new unit still transmits wirelessly and is more affordable for single measuring than TED, but doesn't have some of the fanciness unless you upgrade to TED money.

  30. user-939142 | | #30

    final update:

    Thoroughly tested with the Power factored corrected meter shows the Fujits unit:

    - Uses no measurable power in phantom mode [outdoor unit has power, indoor unit powered off] Meter has a standard error of 4watts; confirmed usage figures with utility meter movement.
    - Uses almost no measurable power in idle mode. [indoor unit powered on but thermostat set far outside need] This model has an economy sensor that may consume a few watts to monitor for movement, so occasionally the meter shows 3 watt; lighted display consumes a little of course.
    -Uses a few watts from a cold start. [outdoor unit off to on, indoor unit off] It appears to go through some sort of boot process for approx 20 seconds.

    Thanks for all the help!

  31. wjrobinson | | #31

    Would love to see a list of units with best wholesale costs, and applicable use which for me would be note cold weather heat capability and warm weather too or warm weather only details.

    Is their one unit the PGH boys in Maine use, cost, and cold specs?

    Enjoyed this thread as I am a fan of energy saving more so than faux green nonsense.

  32. Expert Member
    Dana Dorsett | | #32

    AJ: The Fujitsu AOU-15RLS2-H runs about 2 grand for the hardware (@ internet pricing), and puts out 15KBTU/hr @ -15F, 18KBTU/hr @ 0F, well engineered for cold weather operation. (I guess too many people were messing up their non-H RLS2s running them at low temp, and they figured out how to beat those problems. :-) )

    The Mitsubishi MSZ-FE18NA is similar has ~10% more output, 10% more expensive, but it auto-stops at -18F or so, something to keep in mind if it actually gets that cold often enough to matter. (It automatically re-starts when it warms up a couple of degrees.)

    There are other sizes in both series, but those series(Mitsu- H2i, and Fuji XLT-H) are the only real candidates for locations with 99% design temp south of -5F or so.

  33. user-984364 | | #33

    I put a Brultech ECM-1240 power monitor (which measures real power) on my 12RLS2, and got 10W standby, for what it's worth.

    Hm, on edit - that 10W only lasted for 30 mins. Then it jumped to around 70, and began a very slow decline, 12h later it's around 60W. Strange. Currently very cold out if that matters, but the unit is off at the (single) head.

  34. Expert Member
    Dana Dorsett | | #34

    As I understand it, below some outdoor temperature many mini-split burn current in the motor windings (without turning the compressor) in idle mode to keep the lubrication active, and keep the physical dimensions within tolerances for startup. That could be what's going on with your 60-70W idle here.

    FWIW: The new Mitsubishi M-series H2i ( -FHxxNA ) mini-splits have just been released, and by their published HSPF ratings are something like 15-20% more efficient than the -FE (or Fujitsu XLTH) equivalents.

  35. user-939142 | | #35

    in post 30, I noted with power factor corrected meter, and double checking with the utility's meter, that the unit uses nothing within the measurement error of 8 watts during the warmer months.

    During winter, there is some current use to keep things warm, but generally one would be creating heat so it won't spend much time in that mode unless the unit is sized wrong.

    In rougher environments though, models with a pan heater will burn some significant juice of roughly 60-100 watts almost continuously the whole winter. The Fuj service manual notes the pan heater is on while the unit is making heat except for a small portion of the defrost cycle. The Fuj H model drops form 12.5 to 10.5 HSPF. Personally with my experience I don't see how someone in a 'real' heating environment can go without a pan heater unless you manually help out with and occasional bucket of hot water or such.

  36. user-939142 | | #36

    Looks like that Mits new small unit takes the ratings crown back with a 30SEER and 13.5 HSPF. It also copies the i-sensor in the Fuj.

  37. Veevslav | | #37

    Dont know if anyone figured out a lazy mans power saving for ghost wattage on the mini's, but its really really easy. Its called a line thermostat. The $16 model would work well for it.
    Never having worked with the Mini's I dont know if they have setting retention or not on repower. I also skipped most the comments after I saw someone say it was not possible. But there is the solution.

    Yes I know this is now a zombie thread, google sent me here and since it is still being pointed to by google, I figured someone might be looking for a solution.

  38. wjrobinson | | #38


    let's say I heat a home during the warmest hours instead of shooting for design 8 degrees for my area, design for the most efficient MS (mini split) that will be running on average at 30 degrees, so need it to be at it best maybe at 15 degrees up to 45 degrees? Give up on concern for below 15 due to having super insulated a home, and not doing set back recovery till 12 noon so as to optimize "collecting heat when it is the warmest outside. Warm up the home through the day design sleeping areas below living areas so as to not need to set back at night, via opening a window that way let the heat pump overheat the home which is fine for sitting around evenings. Lifestyle and mini and set backs coordinated to make best use and generate highest COP (ROI too)

    So as of today, what unit to use for roughly 15,000 btus is the most efficient at 15-45 and I guess for the normal way of thinking you already posted what you favor for say 0 degrees design temperature.

    Also who online is selling wholesale that you favor, post this or private email if you wish to ajbuilderny Dana, thank you very much for all the mini split help you have shared for all of us at GBA.

    Mainly my question is, what unit is the best if never asking it to be at it best below 15 degrees F.?

  39. STEPHEN SHEEHY | | #39

    AJ- Just this month I looked into various Fujitsu mini-splits and created a simple spreadsheet from Fujitsu specs that compares total heating capacity ( "T.C." in 1000s of btuh) as well as COPs for 3 sizes, the 9RLS2, 12RLS2 and 15RLS2. I didn't evaluate the H models because the pan heaters use a lot of power all winter.

    The maximum heat output of all three RLS2 units is similar at various outside temperatures. Even at -5, they produce 14,000 btuh or more. The efficiencies between the units vary, but not much, with the 9 and 12 being slightly less efficient than the 15 at very low temperatures, but more efficient once above 14 degrees or so. The quieter sound pressure of the 9 and 12 (21 db vs. 26 db for the 15 at the lowest speed) is important to us, so we selected a 9 and a 12 for our 2 units. Total design load is about 16,000 btuh at 0 F.

  40. jinmtvt | | #40

    Stephen: what pan heaters are you talking about on H models? All RLS2 models defrost using interior heat in backwash mode.. no resistance heating and has very little impact on energy consumption.

    If your temp goes lower than 0c, you SHOULD consider using H models.

  41. user-939142 | | #41

    Jin: Standard on the H series (and optional on some other models) the outdoor unit comes with a heater element in the base pan.

    For those who have to use these things in a real winter environment for some time, when the unit goes into defrost during low temps, the condensate drips down and freezes in the pan (first it freezes over the drain holes blocking the pan up). The ice builds up and blocks efficiency, eventual blocking the fan blades from spinning.
    Probably because the ultra low temp heating is new, not much tech goes into this. The pan heater solution really kills efficiency as its 120 watt element that is on constantly once the temp drops below 40degrees, which for some might last months.

    If you look at the Fuj spec charts, the HSPF drops dramatically on the H models.
    They also don't clearly spell out if there are other improvements, and if there are you can't tell how much things improve as the pan heater throws off the comparison. My guess is there are none as the cooling numbers remain the same, and they should change at least slightly if they upgraded/adjusted other components. Because the standard HSPF is not measured continuously at lower temps, odds are the real world use is even worse.

    Some tech is needed to determine how best to prevent ice build up in the pan.

  42. wjrobinson | | #42

    Pan heater.... pans... could the pan be modified, removed... never looked at one....

  43. user-939142 | | #43

    If you spend a second, you'll realize how silly the question is.....

    The outdoor unit is a box, with a radiator on one end, and a fan on the other. You need the box to direct the air flow, hence you need the bottom.

    One would expect they'd do some engineering to determine how many drain holes and where placed would be optimal so you don't lose efficiency.
    The H models of the Fujitsu did have a different drain pattern - you can check via the repair manuals for the H and non H models. The H models have more holes, smaller, andspaced out. The quicker the condensate can drain out the pan before freezing the better. The non H models have a few holes in the center of the pan.
    My guess is that even with the pan heater, the condensate was still freezing on it's way to the central hole locations.

    Most folks don't experience a problem as temps eventually climb up during the day along with a little sun for a period, and the warm condensate during a fresh defrost cycle will help thaw a hole. But if you go through a week of teens and below, especially with a lot of wet snow fall, the ice build up needs help.

  44. DavidLeff | | #44

    I'm commenting on posts 33 and 34 by Eric and Dana...Dana is correct...Fujitsu's RLS2 series has pre-heat control functionality (as does Mitsubishi GE, FE, FH, etc series) which would explain exactly what Eric was seeing.

    Fujitsu's "Service Instructions" manual for the RLS2 series says the following:

    "When the outdoor heat exchanger temperature is lower than 41°F(5°C) and the all operation has been stopped for 30 minutes, power is applied to the compressor and the compressor is heated. (By heating the compressor, warm air is quickly discharged when operation is started.) When operation was started, and when the outdoor heat exchanger temperature rises to 44.6°F(7°C) or greater, preheating is ended."

    Since Eric was measuring in January, I presume the heat exchanger temperature was less then 41°F.

    Mitsubishi has a similar functionality, although according to a an Application Specialist at Mitsubishi US, it is initially disabled when shipped and is enabled by cutting a jumper wire. The Mitsubishi Service Manual says this:

    When moisture gets into the refrigerant cycle, it may interfere the start-up of the compressor at low outside temperature. The pre-heat control prevents this interference. The pre-heat control turns ON when the discharge temperature thermistor is 68°F (20°C) or below. When the pre-heat control turns ON, the compressor is energized. (About 50 W)

    Prolonged low load operation, in which the thermostat is OFF for a long time, at low outside temperature [32°F (0°C) or less] may cause the following troubles. To prevent those troubles, activate the pre-heat control.
    1) If moisture gets into the refrigerant cycle and freezes, it may interfere the start-up of the compressor.
    2) If liquid refrigerant collects in the compressor, a failure in the compressor may occur.
    The pre-heat control turns ON when the compressor temperature is 68°F (20°C) or below. When the pre-heat control turns ON, the compressor is energized. (About 70 W)

    ON: To activate the pre-heat control, cut JK wire of the inverter P.C. board.
    OFF: To deactivate the pre-heat control, solder JK wire of the inverter P.C. board.
    (Refer to 10-6.1)

    According to the Application Specialist, "discharge temperature thermistor" is an error and should be "ambient temperature thermistor". Even more details provided by the AS say:

    Pre-heat control ON condition
    (1) Compressor is not operating. (However, pre-heat control is still OFF for 30 minutes after compressor is stopped, regardless of the outside temperature.)
    (2) Outside temperature is 68°F (20°C) or below. Outside temperature is monitored hourly, and when outside temperature is 68°F (20°C) or below, pre-heat control is turned ON. When pre-heat control is turned ON, compressor is energized about50 W (40-60 W). (Compressor and fan are not operated.)

    So they both have pre-heat control to protect the compressor. They both wait for 30 minutes after compressor is idle before they enable this "energizing". Fujitsu uses below 41°F as its threshold, Mitsubishi's is a more extreme and uses below 68°F. Fujitsu preheat seems to be on by default and Mitsubishi's is on by cutting a wire.

    I hope this helps anyone else who stumbles on this useful thread.

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