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Whooshing Sound From Indoor Minisplit

DIYJester | Posted in Mechanicals on

I recently had to have the outdoor HX replaced on my Mitsubishi mini split system. During this time the tech recommended raising the unit at least a few inches off the concrete pad to prevent condensate drainage in the winter from freezing up the drain holes on possibly crushing the bottom of the coil (again).

During this time the line set was kinked and another installed. The unit was charged based on their best guesses of the line set lengths (I had purchased lengths and they subtracted a few feet off each end) and used the actual length of the main line going to the branch box.

The commissioning installer failed to write down the original line set lengths or charge amount. The new charge was something like 18.5 lbs.

I am now hearing noises similar to what I heard during the winter defrost cycles, randomly during cooling mode. The other thing I have observed is some slight icing (not blocks of ice) on the suction line coming from the branch box into 4 accumulator and up to the compressor. The compressor has zero icing, and is warm to the touch, including on the suction line at the inlet. I should also note, I have not had any issues keeping the indoors cool and it seems the delta T across the indoor coils is about 20 F (I get that this is just a thumbrule type number).

The company that charged it said they can’t really check superheat or subcooling since it is a system with multiple capilary tubes and linear expansion valves.

Anyone have any thoughts on if this is normal? Maybe my first charge was off and this is ok? I know the whooshing only happened in the past in heating mode (defrost), but I can’t guarantee the outdoor unit wasn’t frosting. I live in Missouri, so having a suction line temperature below dewpoint would be possible but I am not sure. I have my license to do the work on these, but I haven’t messed with any systems other than large commercial systems since I recharged one of the retrofitted R134A units on the training submarine at NPTU Charleston when I got my UCFC.

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