VRVll BSVQ100MAV1 cooling in heating mode

[Thermatech]

Customer complains one indoor unit constantly over cooling & also excessive refrigerant noise.

Unit set for heat mode.
Y3S energized.
Hot gas flows to indoor unit & unit heats for a few mins.
Then Y1S energized.
Hot gas stops flowing to indoor unit.
Suction goes cold & unit cools.
Excessive refrigerant noise.
Y3S still energized.
Unit still set for heating mode but indoor unit cools.

My understanding of this model BSV box is that it has 2 valves.
Y3S is for heat cool change over & is something like a 4w rv.
Y1S is for subcool circuit.

So in heat recovery mode if the indoor unit is heating but another indoor unit calls for cooling then the warm liquid flowing out from the heating unit will be subcooled before dumping into the common liquid line by open the subcooler circuit solenoid valve.

If the indoor unit is heating & the heat / cool solenoid is energized I would expect the box to continue to supply hot gas to the indoor unit not change over to cooling mode while Y3S is still energized.

I have suggested the box needs to be replaced but have not seen this before.
Anyone had this problem before ?

[VRVIII]

Hi Thermatech,

You understanding of the bs box is correct, Y3S is a 3 way valve that will connect the indoor suction line to the outdoor suction on cooling or outdoor discharge line on heating.

Are you 100% sure this is only happening on 1 bs box? when the problem occurs do you hear gas passing from low to high side within the box (3 way valve sticking) if this is the case you would also find a temp increase on the suction line (outdoor side of bs)
If the problem occurs on more than 1 box or different boxes this is more likely to be an outdoor problem (gas shortage/fault exp valve/faulty solenoid valve)

[Thermatech]

I think that the problem is the 3w valve is droping back to the full cooling possition although it is still energized for heating possition.
As the indoor unit opens up the EEV to a much larger opening in heating operation then too much liquid is flushing through the indoor unit making excessive refrigerant noise & the unit has un controlled cooling instead of required heating.

Daikin tech help desk advise change the box as next step as suspect 3w heat/cool valve operation.

But I was just wondering if anyone else has had this problem as I have not personally seen this problem on this model box before.

[VRVIII]

The valve is similar to a standard 4 way reversing valve but only 3 ports are used to divert refrigerant flow, the valve is pilot operated and must have a 4 bar pressure difference (between liquid & suction) to activate the plunger and change mode.

The problem that you discribed is very unusual as when the valve has moved across to the heating position it will normally hold even if the pressure difference decreases (providing the valve fully moved across).

You never confirmed if the problem is only on the 1 box? Also have you monitored liq/dis/suct operating pressures, the bs entering and leaving pipe temps prior to and when the problem occurs. You could also try deenergising and reenergising Y3S when problem occurs to see what happens. Obviously you would hear the discharge pressure blowing through to the suction (which will be loud at 25~30bar HP), have you heard this prior to the unit going to cooling?
When a bs box requires a mode change the outdoor unit goes through an equalisation then builds up liquid pressure to prevent this.
It may be more cost effective in the long run to replace the box as they are sealed units (only the solenoid coils & PCB can be replaced). But I would be interested to know the out come.

[Thermatech]

Only one BSV box with this problem in the system.
Outdoor unit running at 25 to 30 bar discharge & 6 to 7 bar suction.

Hot gas to suction changover after unit has been heating for a while & then subcooler solenoid is energized but main heat cool solenoid is still energized for heat mode.

Dont know if the operation of the subcooler valve is coincidence or part of the reason why the main valve changes back to cooling when it is energized for heating ?

Looking at the box refrigerant circuit diagram & there are a number of check valves / capillary tubes & strainers which pottentially could have blockage.
So perhaps some other problem in the box causing < 4bar diff when subcooler valve opens.

Whatever the problem in the box it cant be repaired so must be replaced anyway.

[VRVIII]

Only one BSV box with this problem in the system.
Outdoor unit running at 25 to 30 bar discharge & 6 to 7 bar suction.

Hot gas to suction changover after unit has been heating for a while & then subcooler solenoid is energized but main heat cool solenoid is still energized for heat mode.

Dont know if the operation of the subcooler valve is coincidence or part of the reason why the main valve changes back to cooling when it is energized for heating ?

Looking at the box refrigerant circuit diagram & there are a number of check valves / capillary tubes & strainers which pottentially could have blockage.
So perhaps some other problem in the box causing < 4bar diff when subcooler valve opens.

Whatever the problem in the box it cant be repaired so must be replaced anyway.

Sorry I was editing previous post after having a think:rolleyes:

If the pressure diff drops when the valve is in correct position it shouldn't make a difference but you could try disconnecting Y1S subcool solenoid and retest to see if it makes any difference. Or you could put all indoors into heating as the Y1S solenoid only energises on a bs box in heating when there is another box on the system in cooling (it may also energise during equalisation/defrost/oil return, I'm not sure about these modes).
It's not something daft like the valve coil breaking down, power contiually going to coil but not continually energising or pcb relay fault causing a voltage drop or poor neutral somewhere. Just a thought.

[cool#9]

I think that the problem is the 3w valve is droping back to the full cooling possition although it is still energized for heating possition.
As the indoor unit opens up the EEV to a much larger opening in heating operation then too much liquid is flushing through the indoor unit making excessive refrigerant noise & the unit has un controlled cooling instead of required heating.

Daikin tech help desk advise change the box as next step as suspect 3w heat/cool valve operation.

But I was just wondering if anyone else has had this problem as I have not personally seen this problem on this model box before.
Hi Thermatec and i'll be so glad to help you in RE forum...

I've had this problem 2 times due to broken 3 way valve.... and i had to change it inside the box:eek: see attachment ( no change from our dealer !!)
Good luck
rgds
cool#9

[cool#9]

Hi
If anybody's interesting of i've had also two month ago a failed EEV on new BSVQ100P opening half a way continuously... the complain was about noisy bs box, i've search and found it after 3 days of investigation...
this service cost reached 2500 € :rolleyes:
Now the noise has disapear and the system run much very well fortunately !
cheers
cool#9

[Thermatech]

Thanks for the info Cool#9
BTW
What procedure did you use to find out that the EEV was constantly fixed at half opening ?

[cool#9]

Thanks for the info Cool#9
BTW
What procedure did you use to find out that the EEV was constantly fixed at half opening ?
Hi
Then after a lot of investigation i tried to fully close each EEV by putting on / off each bs box one by one and one of them did not seem to move ( no noise at closing ). I also try to change PCB and reverse the output of the coils and then still nothing...
I decided to put down the bs and open it, remove the insulation and find out one EEV still open at roughly half a way...you can see it while cutting the copper tube near the body.
I' ve change the whole box of course and the system run very well without any noise...
I.ll try to take some picture soon to show it
rgds
cool#9