Possible reason for VRV III inverter HR not working?

[Lonesurgeon]

Hello experts,

I would like to know the possible reasons for the heat recovery function not working.

Here are the conditions:

Outdoor Temp: 26 C
RH%: 86%
Centralized Controller for Lonworks: DMS504B51
Indoor Unit controllers: Mostly BRC1C62
Outdoor unit: VRV III REYQ12M - R410A
BS: BSVQ100M

I have been told by Daikin HK that the outdoor temp must be below 16C (Wet Bulb temperature) before the heat function can be operated. However, several days ago I set the living room controller to auto changeover at 25C. The indoor temp was 20C so the controller automatically went to heat cycle. All other indoor units were on cooling cycle. Several minutes pasted and I measured the Supply Air vent temperature to be 24C and rising. Soon it went all the way to 27.5C.

Now, I tried to set another room with the same settings. But, it didn't work. And now the living room indoor unit won't work either. The outdoor temperature was the same for the past week with very similar RH (being in Hong Kong). All indoor units are the DQ slims so there shouldn't be a difference. All the BS (3 pipe) are the same. Where's the problem? I don't have a service checker. If I had to buy or steal one I would do it.

I've tried the same settings for all indoor units and none of them would heat (tried overnight). All of them showed the auto changeover once the set temperature was increased. I've tried to force set the heat mode and the results were the same.

Having said all this, my final question is that if simultaneous cooling & heating can only work between -5C to 16C (WB), is it pointless to install this kind of VRV because for most of the year Hong Kong is hot & humid?

Any help on this is greatly appreciated.

[frank]

As your outdoor temperature is above 24C, the heat function is inhibited.

At this outdoor temperature, where your condensing unit is situated, you should not require indoor heating mode, no matter what you set the controller to, it will not heat.