Question on Mini Split in Heat Mode

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  #1  
Old 01-21-15, 01:12 PM
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Question on Mini Split in Heat Mode

Every half hour or so (haven't timed it exactly) my Mitsubishi cycles the directional vanes upward and seems to quit heating for a few minutes. It makes some small popping/creaking noises. Then it returns to normal. Is this usual and what is it doing?
 
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Old 01-21-15, 01:24 PM
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Next time it happens go outside and look at the condensing unit, I'll bet it is in defrost mode.
 
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Old 01-21-15, 01:44 PM
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Thanks, but what do I look for at the condenser? Will the compressor be shut down? The thing is so quiet that I don't know if I could tell.
 
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Old 01-21-15, 01:47 PM
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The fan will not be turning and there will likely be a puddle of water under it. You might even see some frost on the fins.
 
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Old 01-21-15, 02:05 PM
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When I got there, the fan was running, but the discharge air didn't feel much colder than ambient (27). I am curious now, how does this unit defrost? I vaguely understand that in heat mode the AC condenser must become the evaporator and be colder than ambient to extract heat.
 
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Old 01-21-15, 03:00 PM
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My experience with a Mr. Slim was fifteen years ago and that one never went into defrost mode so what I will describe is more generic.

There is a temperature sensor attached to the coils of both the inside and outside units. When in the heating mode the sensor on the outside coil looks for something around 32 degrees and when it "sees" this it will switch the reversing valve and put the inside unit in cooling mode. This is why the direction vanes will move to direct the airflow to the ceiling, to prevent blowing any cold air on the room occupants. The defrost cycle only lasts a very short time, maybe even less than a minute in some cases, and then it reverts back to the heat mode.

What you are experiencing is completely normal.
 
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Old 01-21-15, 03:18 PM
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Thanks Furd

I caught it right when the vanes started moving on the next cycle and rushed outside. The fan was off. That is clever how they cycle the vanes into AC mode for the defrost cycle.

Where I am still confused is that it can't defrost upon sensing 32 because this baby will produce heat down to near zero outside, so the outside evaporator coil must be going below zero at times. I suspect it is really hogging the power in that condition.
 
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Old 01-22-15, 07:06 AM
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I don't know the exact method of determining when the outside coil needs to be defrosted. Sorry.
 
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