Mitsubishi phantom loads

Yeah, chasing things like that you'll need to check the zero & calibration of your instruments, particularly if it's some comsumer-grade thing like a kill-a-watt.

What are you using?

Do you have an outlet near the outdoor unit?
Is anything plugged into it?

Code requires an outlet within 25' of AC unit, I have done the outlet with the AC circuit and using 12-3 cable to get the neutral there.

The load of an outlet connected in this manner goes thru the AC CB.

What type of measuring device are you using and where is it connected?


Note: do you get the same reading if the system is in cool or heat mode?
Perhaps there is a holding coil on the reversing valve drawing power when in the opposite mode of operation.

You have all the indoor units off when you are  getting 220w? What is Mitsubishi saying you should be reading? 

Kind of what I'm getting at... 220 watts is a lot of heat, indeed, and it has to be going somewhere. One of those nasties about energy is that it has a way of winding up as heat, pretty much every time.

Is the unit "OFF" at the tstat or outside at the power disconnect to the unit?

Transformer(s)
crankcase heater(s)
drain pan heater(s)

Most Crankcase heaters are hot all the time.
Drain pan heaters also (if so equiped)
Transformers always have a small current draw.

Thanks Ratio, and pecmsg. That is very helpful. It helps to have as much info as possible before the service visit (so I can "help" them ;-). I will ask about a "crankcase heater"; that wattage would be in the right range, but I would have thought that in summer and after some period of time it would start cycling (maybe) - else get very hot, and this load seems very constant. But all of the suggestions are good and worth asking about. Thanks for your suggestions. I will follow up late in the week to report what the tech tells me.

No solution yet. Service guy found the same 1.3A (240Vac) load I had seen; he seemed competent and didn't think it made sense, but didn't have a spec for IDLE power draw (unit powered but set to OFF). He said he would raise the issue with his Mitsubishi people and escalate until he has a solid answer. I will follow up when I know more.

Hello @Grits,

I'm wondering if one (or more) of what appears to be Insulated Gate Bipolar Transistors (IGBT) that are in IC500 (Red annotation) are electrically leaky. Causing more of a 'Reactive' parasitic current draw. With a 'Reactive' load you won't get the heat dissipation as if it was a 'Resistive' load. DCL1, DCL2, DCL3 (Aqua annotation) are inductors for the power converter for motor power. Also even with the unknown switch or contractor contacts open just above the (Orange annotation) there is a possible current path through the unknown device (Orange annotation).

Not sure if any of this helps you, but I can see the possibility of it happening as you see it on your Ammeter. And I would venture to say it may not be what the original engineering intended.

incase anyone has trouble finding the Engineers response, here they are


From Harry at Mitsubishi
"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."
------------------------------------------------------------------------------------------
"Edward,

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. http://meus1.mylinkdrive.com/viewPdf?srcUrl=http://enter.mehvac.com.s3.amazonaws.com/DAMRoot/Original/10006\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. http://meus1.mylinkdrive.com/viewPdf?srcUrl=http://enter.mehvac.com.s3.amazonaws.com/DAMRoot/Original/10006\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."
------------------------------------------------------------------------------------------
"Edward,

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."

Are there any parts of the circuitry which are live when the unit is "off"? Is there, for instance, an option to turn the unit on by a remote control? If so, there is -- somewhere -- a board which is powered at all times to receive such signals. Is there an option for a wi-fi connection? Is so, that board is also powered at all times. 1 amp sounds a bit much for that, but 100 to 200 milliamps would be quite normal.

I got the power meter today and got readings that make sense. The meter has current, voltage, real power, kWhr, Power Factor. The current was exactly as measured before (1.3A) and voltage was about 244V. What I didn't have before was the Power Factor and real Power. I stand informed ;-) The power factor was 0.06 or below, giving real power in the 20W to 23W range. That is one heck of a poor PF, but it is a small load. As I said, as long as it isn't costing me a lot I can live with this. Still, I wouldn't just leave a 20W bulb going for months at a time so I will probably leave the unit powered off for substantial parts of the season.

Thanks for your thoughts! This is good to know and I will sleep better.

I can recommend this meter (link in a previous post; $24 from Amazon) for cost and functionality; only time will tell how it will hold up.

(I hope this URL is actually a link to the picture I uploaded; should be the meter reading.)

109A_5 - There are control boards in both the outdoor (compressor) part and the indoor air handler part of the unit. I see LEDs. I'm sure some circuits are doing their computing and monitoring. Also, the unit is supporting the RF link to the portable wireless thermostat, even when it is not being called to actively heat/cool/fan. 22W range is acceptable. I think there may be one or more offline switchmode power supplies (like computer supplies) to power the control circuits and these typically have a large capacitor after the rectifiers on the input side (poor power factor...) and a bleeder resistor to discharge that capacitor within a few seconds when disconnected from the line (power loss, but a shock hazard otherwise). I try to be very careful to not waste power but I think this is the unavoidable overhead for a unit like this. I don't know if we can expect anything lower. There is a new generation of switchmode supplies that use a SEPIC topology and that is supposed to improve the power factor, but the need to maintain the control circuits will need some power regardless of power factor.