VRV 2 Cooling in Heating mode

[Darrylfb]

Hi All

I have a daikin vrv 2 r410a, reyq16m8w1b, running 16 indoor ducted units in a hotel, some units share a bsbox some have their own.
Client tells me that usuall late afternoon or evening the units start blowing out cold air.
Ouside air temperature is around 5°c at this time.
I have run this system up fully loaded many times and its usuall heats fine, however, i turned all then units off, and then ran just 6 random units in heating and they all started blowing out cold air to the point the rooms were nearly 14°c.
After speaking to daikin technical, the asked me to change all thermistors and motorised valve heads on the condenser, which i have now done, tested the system after and everything was heating fine. Left site. Got a call following morning from hotel saying they were blowing out cold air again.

This is not specific to any individual units.
If all 16 units are running the issue doesnt occor.
When the issue is present, my condensing unit looks to be operating correctly with running pressures and tenperatures all good, with hot gas flowing to the bs boxes.

Any help would be much appreciated.

[martinw58]

is the system going into defrost

[Darrylfb]

is the system going into defrost

Yes the system goes into defrost, but generally the indoor units fan stop while this happens, and then come back once defrost has stopped.
One of the 4port reversing valves allows hot gas around the lower part of the condenser coil for a few minutes and then re energises for heating mode again.

When the fault occurs the indoor rooms are at 24°c and cold air pumps out continuously and brings the room temperatures down to 14°c.

All units are centrally controlled and locked in heating mode. So a defrost cycle shouldnt occor for long as the system in not under full load.

[martinw58]

where are the return air temp sensors fitted are they sensing the room temp or are they in the ceiling void

[Darrylfb]

They are set to read from the wall controller alone.

[martinw58]

when its blowing cold have you checked what solenoid valves are energised in the box if its always the same units you may faulty pcb

[hyperion]

The units that are affected, are these fed from the same BC box?

[Darrylfb]

The units that start cooling differ, its usually all units currently in operation, the majority of units have their own boxes, only a couple of units share a box therefore i havent checked the bc boxs yet as they are high up and difficult to access.
I revisited this system 2days ago, i swapped pcbs on condensing unit from another identical system at 6pm. Returned the following day at 8am and the issue seemed to have gone, waited with the system all day and at 3pm the issue reoccured... throughout the day people going into their hotel rooms had turned their units off, when the fault occured there were 6 units left on in heating and had all started blowing out cold air while the controller said heat 26°c

[hyperion]

As you have eliminated the control PCB. Could it be a diversity factor that when only 5 or 6 units are operational, there is insufficient index load to get the unit to operate correctly. I have had this when minimum occupation can cause all sorts of strange effects. I believe that the VRV system needs 35% loading request before it will work properly. Check with Daikin or request a site visit.