Mitsubishi Mini Split Hyper Heat hissing sound in lineset when in heat mode

agold2009

When turning on the FS06 6K BTU Hyperheat, I hear a hissing sound coming from the lineset in my closet. Its a high pitch hissing sound which goes away after around 5-10 minutes when the unit heat ups. I'm assuming its the gasses in the linest, but is this normal?

Ironman

How was the unit charged with refrigerant?

EdTheHeaterMan

It takes at least 5 minutes of run time for any refrigerant system to get to the balance point in the steady state operation of the system. So that noise may be normal.

The hissing is the refrigerant in its gaseous state traveling through a restrictor of some type. Once the liquid state refrigerant is fully charging the liquid line, then the hissing will stop. Just a poor choice of refrigerant line location. Have you tried "Alexa... Play white noise while I Sleep"

agold2009

Ironman said:

How was the unit charged with refrigerant?

It wasnt, the lineset run is less than 25feet so the refrigerant was just released into the system off the condenser

Ironman

Is it a single or multi zone system?

agold2009

Ironman said:

Is it a single or multi zone system?

Single. Can this be caused by too much moisture in the line?

EdTheHeaterMan

Did you evacuate the refrigerant lines to 500 microns before opening the service valves?

if not, there could be a moisture problem 

agold2009

Yes around 190 microns held for over 10 minutes.

The techs nitrogen regulator was busted so he used a quick burst of compressed air first to clean out the lineset of any debris from the reaming of the flares. Then vacuumed down to the 190s before releasing. I’d imagine there was some moisture introduced with the compressed air but I’d imagine the vacuum would get rid of it

Heree a video of the sound 

https://youtu.be/5jSu0eDqEM0

EdTheHeaterMan said:

Did you evacuate the refrigerant lines to 500 microns before opening the service valves?

if not, there could be a moisture problem 

pecmsg

agold2009 said:

Ironman said:

How was the unit charged with refrigerant?

It wasnt, the lineset run is less than 25feet so the refrigerant was just released into the system off the condenser

So if the outdoor unit was short of refrigerant?

190 Microns, that's highly improbable. In 10 mins it should have risen a little bit, if there was moisture in the lines a lot!

Ironman

Compressed air??? That’s just about the worst thing he could have done.

It’s obvious that you didn’t have a qualified technician.

The entire charge should be removed, the system be triple evacuated to 300 microns, and then be properly charged with virgin refrigerant weighed in.

agold2009

Ironman said:

Compressed air??? That’s just about the worst thing he could have done.

It’s obvious that you didn’t have a qualified technician.

The entire charge should be removed, the system be triple evacuated to 300 microns, and then be properly charged with virgin refrigerant weighed in.

Yeah I agree wrong thing to do. But if he did the vacuum wouldn’t that essentially remove any moisture introduced by the compressed air 

EdTheHeaterMan

I have a personal record of 40 years with no compressor burn outs. (mechanical failures don't count as burnouts). Back in the day there was a procedure called triple evacuation. That is how I was taught to remove moisture from a refrigerant line. We would use R22 to purge and blow out the line (before EPA regulated this practice) then evacuate, then R22 then evacuate, then R22 then evacuate, then open the service valves. After doing it this way for several years I took a RSES course and found that R22 will just cause the moisture to freeze in the line set and may not completely remove it. Dry nitrogen will be a better gas to purge with. after that course, I purchased a Nitrogen bottle and a regulator. But until i retired, I still triple evacuate (with nitrogen). Never had a warranty burn out of a compressor. Many installs by me were service agreement customers and I never replaced a compressor on one of my installs.

I guess I could have been less of a stickler on that detail and made some money on the labor of replacing compressors under warranty in the 3rd and 4th year of the service agreement. But I'm just not built that way! "Do a good job for a fair price" was the family business motto. We were never the lowest bidder, but we had a reputation for good work.

So compressed air is not the best practice for refrigerant line installation.

Did I ever tell you about the plumber that leak checked his refrigerant lines with water? What else would a plumber use?