Mitsu heat pump squealing sound

[Weissenheimer]

New here (so new I can’t post a link yet, work with me). Not sure if this forum is exactly the right place but I am curious what you all think about my issue. I have a Mitsubishi dual zone hyper heat mini split system to heat my work shop in the basement. It started making an awful squealing noise (YouTube video: add this—> https:// before this —> youtu.be/wCfAQlXBGoI ). Appears to only do it on the “defrost cycle” as I understand, or right before it hits temp and begins to turn off. At first I thought it was the blower fan, but it doesn’t let me change the speed when it is in the middle of idling down. Although when I leave the fan speed on low it did not appear to make this sound any more. 1st idea is bad bearings but it just seems too predictable that it only happens near the end of the heating cycle. 2nd idea I am thinking what I’m hearing is a high frequency vibration being sent through the refrigerant lines related to the length of pipe. I have heard grumblings both yay and nay about there being a min length of pipe (online). But Mitsubishi told my hvac guy they recommend 16 ft min. This head unit (6k btu) has the shortest run of pipe of all my heads (6ft). It is also on the same pump as another head (18k btu) with 20ft of pipe.

Note, my hvac guy is going to (somehow??) add a longer length of pipe this week. Not sure if thats the path I would take yet if I was doing it. I still haven’t seen him pull out the blower fan or check pressures (easier stuff than pressuring down and adding a coiled pipe outside the shop...because I have heard coiled pipe can trap oil and kill and pump prematurely...). What a mess, but I hope it works. You know the saying, “trust the professionals or you’ll go nuts WebMD-ing yourself”. It appears I am a guinea pig and no one else has this issue. I’m thinking one-off Covid quality control related issues?

 

[Jackfre]

In ‘06 when the the inverter 410A units came out I represented Fujitsu in the 6. New England states. We were instructed that there were minimum line set lengths. That first year they said with to short a line set you could turn the Evap into a speaker. We received no better tech description at that time and we were only beginning to understand the capability of the inverters. The following year I was at the big trade show and engaged one of the Japanese engineers in discussion on this topic. “Okay, it can turn the evap into a speaker, but what is really going on.” He calmly turned and said, “It is the compressor tearing itself apart...slowly.” Do not let you or mechanic loop a coil of pipe. It will trap oil in the loop. Have him lay it off in a serpentine fashion. A couple pieces of unistrut will make an excellent support for the pipe.

 

[Weissenheimer]

Thank You! This is the best answer I have had regarding if my thoughts are correct. Maybe my installer just hasn’t had this issue before and never realized there is indeed a minimum line set distance and also a certain way to extend that. We will see tomorrow when he does it fingers crossed

 

[Weissenheimer]

Well...he showed up before I got home and already coiled the pipe........too early to tell if it fixed that sound, and it will be a while before I find out if coiling the pipe is killing my compressor. I will keep this post updated

 

[Jackfre]

I would suggest that you reach out to the local factory rep on this topic. I no longer have his number or contact info. Mitsubishi has a man in Maine. If I am wrong on this, no harm no foul, but if your dealer is wrong you end up in a jam, potentially. My mini-splints are 14 yrs old and no issues. Yours should/will last at least as long if the install is correct. Did the additional pipe length solve the noise problem? Tell Roger that Jack said hello.

 

[Weissenheimer]

I would suggest that you reach out to the local factory rep on this topic. I no longer have his number or contact info. Mitsubishi has a man in Maine. If I am wrong on this, no harm no foul, but if your dealer is wrong you end up in a jam, potentially. My mini-splints are 14 yrs old and no issues. Yours should/will last at least as long if the install is correct. Did the additional pipe length solve the noise problem? Tell Roger that Jack said hello.

It lasted a few days but started making the noise again... So unless running a short line set permanently damaged the unit, I guess it is just a defective head. I really think I got a lemon whether it is Covid quality control related or not.