Fujitsu Evaporator Freezing when turned off

cheftim_2

I installed a Fujitsu AOU18RLXFZH condenser and 2 ASU7RLF1 evaporators for a 24x28 2 story workshop I built (1 evap upstairs 1 downstairs).

I don't use the one upstairs at this point.

When I turn on the lower one and it's running for about a day or so, the upstairs one freezes up and drips all over the floor. I've tried to get some pros out to take a look at it but no so easy where I live here on Cape Cod.

I explain the situation to them and they all say the same thing: It most likely needs refrigerant because units can freeze without enough refrigerant. I then question that logic based on the fact the upstairs unit is freezing but it's turned off so do they still think it's a refrigerant issue. Not much said at that point and I don't hear back from them again.

I would imagine there's a valve involved at the condenser side that is allowing refrigerant to flow to the unit that's off and that's somehow contributing.

Any and all feedback appreciated. Just trying to get looking in the right location to find the source of the problem.

cheftim_2

Oh, and if there's anyone on the Cape or nearby that could be recommended, I'd rather have a pro look at it.

ratio

With all the multi splits I'm aware of, the outdoor unit never turns the refrigerant completely off, even to a head that is switched off. I suspect this is for oil control. Maybe try leaving it on but set up pretty high.

Big Ed_4

I would first check the connections of the control wires , my guess they are connected wrong in the condenser ..

cheftim_2

@ratio You're saying turn the upstairs unit on (the one's that's off but freezes) any time I turn the lower one on?

@Big Ed_4 If they are connected to the wrong points on the condenser, is it possible the lower one would come on as it does?

Big Ed_4

Seems like to me , two wires power the inside unit and the third is the communication to the condenser . Maybe it was wired wrong from the factory if not wired wrong on your part . Seems like the control wire terminals are switched . I would be calling tech support to verified . Mistakes are made

ratio

Yes, just set it to cooling to 85°or something, just to see what happens

I had a multi-split (4 heads) freeze up when the heads were wired one port off. (wired to A, B, C; & piped to B, C, & D) It just so happened that one of the heads had a small load & didn't need to run often, but the others basically ran all the time.

Big Ed_4

Raise the upper and see if the lower gets cold , then you will know....

mattmia2

Is there maybe some minimum flow thing that opens that zone too when only 2 zones are calling?

GGross

mattmia2 said:

Is there maybe some minimum flow thing that opens that zone too when only 2 zones are calling?

Generally multi split outdoor units have a minimum operating range, and that minimum changes depending on the number, size, and type (ducted, ductless etc) of indoor units connected. This is not always clearly stated in the machines spec sheet, they will usually show the rated minimum which is the lowest possible that the unit can run at, based on the minimum connected units.

LG has engineering manuals for their multi head units, and design software, that when used properly can identify these issues before installation. The issue I see is that almost nobody uses these tools, they just see the minimum on the spec sheet and base the design off of this number.

If needed the ODU will force indoor units that are not calling to do something to dump the extra load

mattmia2

I meant one zone calling, but you got the idea.

pecmsg

Lines crossed
electrical crossed
short of refrigerant 

HVACNUT

Multi head systems, when sized and matched correctly can absolutely operate with just one head running. Refrigerant will flow through the other heads even if they're off, but the coils shouldn't freeze. Agree with @pecmsg. One of those 3. 
Do you know if the total line set length exceeds the factory charge, and of so, was X oz. added per ft.?

cheftim_2

I appreciate all of the feedback. Managed to come down with Covid a second time but I will try and get out and look at some of the suggestions including electrical lines issue and minimum heads running in a multi zone unit.

rsilvers

You could also check if the 4-way reversing valve is working.

cheftim_2

Got out to the workshop where both systems are off. Set upstairs to high temp downstairs to low

Upstairs
Initial temp 79
Set Temp: 80
4 hours later: 66
Temp of evaporator air measure with Fluke IR 52

Downstairs
Initial temp 74
Set Temp 66
4 hours later: 72
Temp of evaporator air measure with Fluke IR 74

Sounds like the control wires are crossed maybe?
As simple as just flipping them at the condenser connections and see what happens?

pecmsg

cheftim_2 said:

Got out to the workshop where both systems are off. Set upstairs to high temp downstairs to low

Upstairs
Initial temp 79
Set Temp: 80
4 hours later: 66
Temp of evaporator air measure with Fluke IR 52

Downstairs
Initial temp 74
Set Temp 66
4 hours later: 72
Temp of evaporator air measure with Fluke IR 74

Sounds like the control wires are crossed maybe?
As simple as just flipping them at the condenser connections and see what happens?

Where's the installing contractor?

Big Ed_4

That's another story

rsilvers

Your outdoor unit has electronic thermal expansion valves to meter how much refrigerant each room unit gets. Seems like it is not shutting off flow to the upstairs unit. That could be a wiring mistake or a EEV problem.

pecmsg

rsilvers said:

Your outdoor unit has electronic thermal expansion valves to meter how much refrigerant each room unit gets. Seems like it is not shutting off flow to the upstairs unit. That could be a wiring mistake or a EEV problem.

If that was the case a trouble code would be generated!

rsilvers

pecmsg said:

If that was the case a trouble code would be generated!

Maybe a trouble code is being generated. Or maybe it is wired wrong. Mostly I was saying that I do think this unit can control the flow of refrigerant to each head unit and that the flow doesn't normally go through units not calling for cold.

cheftim_2

I'm going to retrace the wiring this morning to further check my assumption the controller wiring is wrong. The system hasn't really worked correctly since the installer, yours truly, installed it a few years back. I'm not in the workshop a lot and when I am it's not for long periods of time and will often turn on upper and lower heads.

Seeing the heads go to the set point of the other remote feels like it's the controller wiring. I'll report back. And as usual, thank you to all of you for taking the time to respond.

HVACNUT

It certainly seems like the wiring is crossed. That's why they make ohm meters. 

cheftim_2

Yup, flipped those controls wires and everything working like a charm. Thanks again for the help.