Daikin RZQ200 Defrost issue

[Peter_1]

I have a RZQ200 on a OEM coil in an AHU which starts a defrost at an ambient of -5°C, Te at -11°C every 27 to 30 minutes but there's not a single drop of ice on the coil. The defrost then lasts >15 minutes and it takes then +/- 7 to 10 minutes before coil is hot enoiugh to start the fans.
What triggers faulty the defost in this case? Charge is OK.
We've taken IR-scan during the defrost and after 5 to 6 minutes, the whole coil still is at -1°C. I have pictures of it.

[flyinkiwi]

Faulty coil thermistor, perhaps?

Is your 4-way valve changing over correctly?

[install monkey]

Freeze protection function
Start Te ≤ -1°C for 40 minutes
accumulated
OR
Te ≤ A°C for 1 minute
continuous
(Indoor decision)
Te ≤ -1°C for 40 minutes
accumulated
OR
Te ≤ -3°C for 1 minute
continuous
(Outdoor decision)
Te ≤ -1°C for 40 minutes
accumulated
OR
Te ≤ A°C for 1 minute
continuous
(Outdoor decision)
End Te > 7°C for 10 minutes
continuously.
(Indoor decision)
Te > 7°C for 3 minutes
continuously
OR
Te > 4°C for 20 minutes
continuously
(Outdoor decision)
Te > 7°C for 3 minutes
continuously
OR
Te > 4°C for 20 minutes
continuously
(Outdoor decision)

[Peter_1]

Thermistor was checked by Daikin itself and the 4 way is 100% working. It's the trigger for the defrost that botters me.

[Peter_1]

I.M., what's Te ≤ A°C for 1 minute?
As far as I can conclude now, there's no real detection if the coil is iced up at all. We can run under the present conditions at least 3 hours before we need a defrost. We're losing now a lot of energy and I'm wondering in how far this was considered in the overal COP of the machine!

[marc5180]

Hi Peter I think A°C is the 'timer A'. In other words what ever the defrost interval settings are at.
These can be changed by using 'mode 2' on the outdoor unit.

[r.bartlett]

http://daikintech.co.uk/Daikin-Zoom/Split-Sky-Outdoor/RZQ-CY.html#

manual here

[Peter_1]

http://daikintech.co.uk/Daikin-Zoom/Split-Sky-Outdoor/RZQ-CY.html#

manual here
Thanks Richard, I think I will need someone form Daikin to check and more specific to monitor while running at low ambients trying to analyze what triggers the un-needed defrost cycle wand why it last such a long time before we reach end defrost. There as too much variables to monitor finding out what's happening.

[r.bartlett]

Are you sure it's defrost and not oil recovery ?

[Peter_1]

It's 100% for sure a defrost Richard (even Daikin followed once this machine) + sign on remote controller indicates defrost + 4 -way valve reverses and we took several IR-pictures while unit defrosted. Can post those. Takes a long time before defrost ends: 29 minutes running, shut down for a defrost and then +/- 22 to 24 minutes before units blows heat again. Not that good for the SCOP or SEER I presume.

[r.bartlett]

Most defrosts are a version of the old

instigate defrost
Time+ temperature

Terminate defrost
Time or temperature

If this isn't happening it's most likely the board...Rough part changers guess but from where I am sitting it's my best shot :-)