Mitsubishi minisplit recovery after power outage
My wife and I still heat our house with a wood stove, but we have installed a Mitsubishi ductless minisplit in the living room for backup heat when we are away from the house during the winter. I don’t have a lot of experience using it yet.
I recently turned on the minisplit and it didn’t work properly. I called the installer, who suggested the same fix that is suggested by computer repair people to solve all problems. (In the case of a laptop, the solution is to turn off the laptop, count to 10, and turn it back on again. In the case of a minisplit, the solution is to turn off the circuit breaker, count to 10, and turn it back on again. The solution worked for the Mitsubishi minisplit.)
The installer’s explanation was that, in the case of a power outage (we had one a few weeks ago), a power surge or power glitch that occurs when the power comes back on can confuse the Mitsubishi’s electronic circuits. Hence the need to turn it off and start again with clean electricity.
This was a long introduction to my question: Can anyone who owns a Mitsubishi minisplit share your experience with whether the unit recovers from a power failure smoothly? In general, will the unit come on automatically when power is restored? (The official answer from Mitsubishi, as far as I know, is “yes,” but I’m looking for a real-world report rather than the results of a lab test.)
My worry, of course, is that we will be away from the house for two weeks, and a power outage of a few hours will occur while we are gone, and some problem prevents the minisplit from re-starting.
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> I recently turned on the minisplit and it didn’t work properly.
Could you elaborate on this, please?
Patrick,
The point of my question has nothing to do with that problem, which was easily fixed by turning off the circuit breaker and turning it back on. The point of my question has to do with whether or not a Mitsubishi minisplit will dependably turn back on after a short power outage.
But, to answer your question, the indoor unit's louvers opened up and the unit began to hum. After an hour, the indoor unit's fan still hadn't come on, and no heat could be felt with my bare hand near the louvers. A trip to the outdoor unit revealed that the outdoor unit was humming but the outdoor unit's fan wasn't turning. The circuit breaker off-and-0n trick was all it took to get the system working properly.
Hey Martin,
The reason I asked about what it was doing was that I was trying to envision a behavior that could be caused by a power outage that was two weeks prior (since that's the one you referenced). I certainly think the voltage sag theory has merit.
Maybe other folks familiar with Mitsubishi equipment could chime in... I wonder if there are any states the unit could get into which could result in showing an error code on the hidden LED display in the outdoor unit but not showing anything on the indoor unit to alert you to go look. Could be worth knowing this in case the situation happens again. If it's a possibility, you could pop the cover off and go look.
Martin, I'll offer up anecdotal evidence: ten years of Fujitsu minisplits in my house, and several years of Mitsubishi units in rental properties, and I've never experienced what you describe. They've all restarted automatically just fine after being off for months seasonally or after power failures ranging from flicker to hours. Mitsu P- and M-series have an internal setting (#1, actually) that toggles between restart modes, but that doesn't sound like what you saw. To be truly secure, maybe you need a backup to your backup, or you could use one of the WIFI thermostats to monitor while away (which, of course, is vulnerable to router problems...)
Andy,
Thanks very much for your helpful information. I recently received in the mail, and installed, the Kumo Cloud module that allows for remote monitoring of the indoor temperature. (Due to supply chain issues, the module was unavailable for quite a while.) So that will be one way for me to monitor the situation.
I'm very glad to hear of your history of success. Thanks again.
The unit will almost certainly have a hold off timer that is designed to prevent the compressor from operating for sometime after a power interruption.
Martin how sure are you that was not in timeout mode?
Walta
Walta,
Pardon my ignorance, but tell me what you mean by "timeout mode."
A compressor could be damaged if the compressor is restarted before the high and low pressure inside the system have time to equalize. The control system starts a timer when the system turns off the compressor. On power up after an outage the system can know how long it has been since the compressor was running so it runs a time out cycle on power up before energizing the compressor.
Walta
Walta,
Do you know the maximum length of the time out cycle?
Manual says it's 3 or 4 minutes depending on the model.
3 minutes is common but some are up to 15.
Walta
Walta,
I waited over an hour -- and the unit still wasn't functioning. It was just humming.
The unit itself can't differentiate between you turning off the circuit breaker and the power going off. What I think you're seeing is not so much the result of the power going off as the result of a very quick dip in voltage.
You write: "the outdoor unit was humming but the outdoor unit's fan wasn't turning. " Normally that would be a classic symptom of a failed start capacitor. Electric motors take more current to start from a stop than they take to run; a start capacitor allows the motor to briefly consume more power than it normally can handle in order to get up to speed. The motor has a centrifugal switch that opens once the motor reaches a certain speed and disables the start capacitor.
If the motor is running, the power is cut, the motor slows down but then the power is restored before the centrifugal switch closes again, the start capacitor is defeated and the motor won't start up again.
DC Contrarian,
Thanks for your comment. Your explanation makes sense.
You wrote, "The unit itself can't differentiate between you turning off the circuit breaker and the power going off." I know that, which is why I described the possible cause of the problem (using not particularly technical language--reflecting what the installer told me) this way: "a power surge or power glitch that occurs when the power comes back on." The "power glitch" could be, as you speculate, a dip in voltage.
DC's idea is in the right neighborhood. These mini splits don't have any capacitor start/run motors, all of them are either brushless DC (compressor) or 3 phase induction (fans).
To drive the compressor most (all?) use a sensorless system which generally needs the compressor to start from zero and ramp up to speed to keep it in lock. With a temporary power blip, the compressor could have gotten out of sync with the drive signals which would cause the rotor to stop and oscillate back and forth which would make a loud hum. It sounds like this is what happened.
Unfortunately this probably falls into one of those corner cases the engineers didn't look into or would be hard to fix.
In the industrial world you can get power monitoring relays for equipment. These can be configured to disconnect the system in case of a power brownout situation, not sure if it would be worth the cost.
If any of your old PV stuff is grid connectable (ie Outback GT or Schneider SW), those also work great as a full house UPS. Putting the heat pump on the battery backed up circuit would filter out these power blips.