Daikin REYQ12M7W1B Defrost

[woody100]

Hello, I am working on a Daikin REYQ12M7W1B which has 16 fan coils attached to it. During operation everything appears fine to start with but after 5-10 minutes the system stops with no fault indicated, and then re-starts and goes through the process again. The last time it happened I was next to the condensing unit and it seems the units is defrosting after 5-10 minutes of every start even though the coil is clear. Does anyone know what initiates the defrost? is it outdoor coil temp, suction/discharge saturation temp or either.
The system is running on R410a and prior to the defrost the discharge pressure did not go above 310psi and tended to hover around the the 290psi mark. Suction pressure was 70psi.

[woody100]

Hello me again, I forgot to mention all of the indoor units were calling for heating

Thanks

[Airconking]

I think defrost is controlled by outdoor air temp thermistor/coil thermistor. Sound like
You have a faulty sensor. Phone Daikin tech and they should be able to tell you what
Resistance you should be getting on the thermistor at a given temp, from this you will be able to check each thermistor.

[woody100]

Thanks for the reply

[woody100]

The indoor units are GUFs. The internal box filters were dirty so we removed them and cleaned them as best we could on site. This made a big difference to the air flows to the room but the discharge remained high. Didn't realise that the fan speed altered according to coil temp, i thought it responded to room temp, I shall check that on my next visit. Does anyone know which LEVs expand the refrigerant prior to the outdoor coil when in heating?

[woody100]

Please ignore the last post i'm getting my threads mixed up!

[martinw58]

are you getting full heat from the units if not might be short of gas