Mitsubishi mini split squealing

Weissenheimer

I had hyper heat mini splits installed last summer. No problem with AC but it was near the end of the season so didn’t use it much. I don’t rely on them for heat on the main floor either. But I do use them in the basement for everything. Since install most of my use has been heating the basement this winter. Background on my setup: Two heads on each side of house sharing a compressor. But sized to add a third on both systems for upstairs. The one I’m having problems with is my 6k unit (smallest one) which shares a pump with my biggest unit (18k) upstairs. Note, that small head also has a short run of pipe (12ish feet). Not sure if this is related to my problem? On defrost cycle if I am upstairs I can hear (through the big head) what sounds like a toilet flushing. That sound isn’t my problem, but may be related to the main one. My hvac guy has mentioned potential issues with the length of pipe in a system. Anyway, It is an awful squealing sound which to me sounds like bearings in the cage fan.  But it is suspicious that it seems to do it only right before it hits temp and begins to idle down. Wondering if it refrigerant related/internal but still think that is unlikely. Because While it is squealing, if I adjust the fan speed it doesn’t go away but does appear to change pitch/loudness! I posted a link to the video below. Note in the video I don’t change the fan speed.  My hvac guy is stumped and he sent my video to a rep. Haven’t heard back yet but I thought I’d share my problem here because it seems rare. I am wondering if it is a Covid quality control issue...

here is a link to my YouTube video of it: https://youtube.com/shorts/shZd6BH0XRU

GW

Did he try taking the blower wheel out and lubing each end? That would be step number one, it’s pretty simple

Weissenheimer

He did not do anything the first call back except scratch his head. 2nd call back I coaxed him to open it up and at least check for anything obvious. He didn’t find anything but I did not see the blower wheel come out either. As of today I am now heating the house with just mini splits to see if it has something to do with it, somehow. 

GW

Ok there’s no expansion valves, so I predict the blower wheel is the problem. Order a new wheel and new grommets and lube them with plumbers grease, I bet that’s all it is 

next time you fire that thing up- with your remote control: change blower speeds with the remote and see if the noise changes. That will confirm. The outdoor unit won’t respond quite as fast as the blower will do the change in noise should be instant 

Weissenheimer

GW said:

Ok there’s no expansion valves, so I predict the blower wheel is the problem. Order a new wheel and new grommets and lube them with plumbers grease, I bet that’s all it is 

next time you fire that thing up- with your remote control: change blower speeds with the remote and see if the noise changes. That will confirm. The outdoor unit won’t respond quite as fast as the blower will do the change in noise should be instant 

Fan speed does not matter at all. I finally caught it on video as it begins to make the noise though! It might explain some things. You can hear crinkling in the head as it cools down/enters defrost cycle so I think it is related to this specific event. Intense high frequency vibration is sent through the head causing this noise, not the blower fan itself. As far as I can tell. Also, not captured in this video I tried adjusting fan speed while it makes this noise and it won’t let me as the system is in the process of turning off because it reached temp. I appreciate your insight!

EDIT! What are the odds, my hvac guy got back to me saying mistubishi contacted him. They recommend a 16ft minimum on pipe length and I have 5. They believe this is the problem, as I have been concluding myself lately. He is going to somehow make the run of pipe longer this Friday..hopefully it doesn’t look awful outside...either way if it fixes it then I will be thrilled. 

https://youtu.be/wCfAQlXBGoI

GW

ah wow I haven't had this issue yet. Multi zone system?

Weissenheimer

GW said:

ah wow I haven't had this issue yet. Multi zone system?

I’m running two multizone systems 

Weissenheimer

GW said:

ah wow I haven't had this issue yet. Multi zone system?

So my hvac guy lengthened the line set and also coiled the pipe to do so. Too early to tell if it fixed it but I will keep this post updated. One question though, I have heard that running a coil of line will prematurely kill the compressor, as the refrigerant will separate from the oil. Not sure if you have any knowledge of this? 

pecmsg

There are minimum line set lengths, not sure what Mitsubishi requires. 

I hope that coil is horizontal and not vertical!

Weissenheimer

Weissenheimer

It has been a week but the unit started making noise again....unless running a short line set permanently damaged the head, I think it is just plain defective whether it is Covid quality control related or not

GW

Not sure it’s supposed to be looped like that. Have you determined when it happens and when it doesn’t? It’s common for multi zones to send gas to an “off” zone which creates some noises. It’s clearly spelled out in the manual 

pecmsg

Weissenheimer said:

That is the wrong way to run a line set!

ratio

The drain hanging out from the line hide isn't very attractive, either.

Weissenheimer

ratio said:

The drain hanging out from the line hide isn't very attractive, either.

That, and my back porch stairs will be landing right below the drain, So I will have to extend that drain to the ground when I get to it

kateh234

Did you end up resolving this?! We have two units making a similar noise. Our HVAC technician is looking into reacement of belts and bearings....but I'm not certain that the fan has anything to do with it. I have a suspicion the i-See unit has an issue. Either way it wakes up the household at night. 

Edit! Also this post was the only instance I was able to find online that seems to match the issue and sound our units are making. Ours is a different model but Mitsubishi. Installed in 2019 and 2021. 

Steven_G

Im wondering if either of you ever resolved the mini-split squealing issue. I'm having the same issue. its intermittent, happening only when my tenant is asleep. I tried changing the fan motor. But the noise is worse. so far its only happening in one indoor unit. I dont see any icing. on the fan coil fins. The lineset is is long and refrigerant has been added to compensate for the length. The previous tenant never complained.