[Brett L.]

Hello, this is my first post so I just wanted to take a minute to introduce myself. I've been in the HVAC field for about 22 years now, most of those years have been spent as a mechanic doing new installs. Also spent a few years doing strictly oil to gas conversions. I have all the basic service knowledge but haven't spent a whole lot of time doing service work exclusively, especially on dual zone mini splits. I've installed probably 10-15 single zone mini splits over the years but never a dual zone.

I bought a cape cod about five years ago and installed two indoor units matched with one outdoor unit. They have been working fine for about four years now, up until last week. The two indoor units. (A) 3 year old daughters room, and (B) a playroom. Well, the A unit started making strange noises in the middle of the night, thus waking up said 3 year old and causing us misery the next day over lack of sleep. B unit continues to work fine, even though that room is barely being used. ☹
I finally get some time to check out what's going on, and discover a small leak at B unit's indoor flare connection. No idea how this came loose after 4 years. Also, i find it odd that the unit with the leak works fine and the other does not. I recover the refrigerant, blow through all four lines with nitrogen, then pressurize the system with 200 lbs. and let it sit awhile. Two hours later no movement on my gauge so I pull a vacuum on both A and B lines, then weigh in the 4lbs 14 oz r-410a, the amount it was shipped with.

With Indoor B unit on and A off, everything works fine.
With both indoor units calling for heat, B continues to work but A indoor operates at a low fan speed blowing cool air.
With just Indoor unit A calling for heat and B off, it will still not heat, indoor fan operates at a very low speed blowing cool air until indoor unit started flashing a 10-1 code,
Outdoor unit discharge temperature error.

It just seems the outdoor refrigeration A lines won't get hot like there is an obstruction, but I don't see how this could be possible. B unit 3/8 line gets nice and toasty. It's just a little confusing to me because they are both working off of the same compressor. I know there are no leaks. Also, indoor unit A fan works at all speeds when I turn it to fan setting so I know I'm good there.

I would really appreciate any tips or suggestions on how to resolve this issue from someone who may have run across this same problem working with dual zones. Sorry for the long rant 😞



Sent from my iPhone

 

[hvacvegas]

usually that code is a refrigerant issue.
The hot gas isn't hot enough, or too hot.

Find fujitsu's tech tips on checking EEV's.
Check your EEV sensors.
Check for frosting.

I'll assume your within your lineset guidelines?


Usually, one head working fine by itself (both heads), but the second one that comes on NOT working, is lack of refrigerant.
One not working at all, is a restriction.
It may be restriction that the board has created, because of sensors out of range, so don't go pulling out things to check for restrictions until you've checked your electronics.

Indoor fan speed is determined via the indoor coil temp thermistor. The coil has to be a certain temperature before it allows it to ramp up.



To give you an idea.
I've replaced 1 EEV valve assembly.
I've replaced tons of sensors and EEV heads.

The inner workings of these units are very complicated. It is a billion times harder to troubleshoot and repair than install.
You are working with technology you may have never even heard of before, even with 22 years of experience.
I've repaired/installed these units for roughly 8 years, and just found out last week they are using "voltage reactors". Something I have no idea about.

Calling fujitsu for help may be wise. It's more common than you would think.
The only problem is, that you need to be halcyon registered (training), or they may not help you.

 

[Gunslinger]

I shake every time I have to service one of these. Loss of refrigerant to a common problem.

 

[Brett L.]

Thanks a lot for taking the time to reply. It's a breath of fresh air hearing from someone who knows these things.

If indeed this issue is being caused by lack of refrigerant, can you explain why one unit and not the other always works individually? If I shut down unit B, the one that works fine, then shouldn't there be sufficient refrigerant for A to operate the way B does if B is off?

When these were installed additional refrigerant wasn't added (unit came pre charged at 4lb 14oz) so after I found the leak that's exactly what I weighed back in. Also, in the manual it states this unit can handle up to 98 feet of line set. I re measured and it looks like the lines are around 70 feet combined.

I will definitely try speaking with a Fujitsu tech my next go around with this issue. Thanks again!

 

[jnsrose]

Tech support is your best friend when it comes to minis.
Sounds like a sensor or EEV or LEV like stated above. Only problem is finding it.
Have you tried it in cool mode to see if problem is the same? I had same problem with a system I installed, although it was Misubishi not Fujitsu. After battling for a while tech support and warranty replaced outdoor unit.

 

[Brett L.]

Jnsrose, south jersey here also! When I got home from work today it felt around 55-60 degrees. I followed your advice and tried both units in cooling mode.
Well, same issue is occurring, unit B comes on right away and blows really cold air. Unit A indoor fan comes on and blows strong air (fan setting on auto) but it isn't cold air ��

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[madhat]

We have one that has four inside units to one outside unit. Had a leak at the third unit from the outdoor unit on the flare connection, unit was repaired and recharged. Forth unit wouldn't heat or cool. It was under warranty, and the tech. was pulling his hair out trying to get it to work. We had power outage a couple of nights after, and it has worked ever since. Asked if he'd cycled the power after charging the unit and he couldn't remember whether he had or not. BTW you are supposed to use a Specific flare tool, and flare torque wrenches on the units.

 

[hvacvegas]

Sounds like you need to get in there with some tools. Start checking.