Daikin UATYA-B, Operation Manual

Page: 53 / 126

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Service manual Daikin R32 Rooftops UATYA-B
ESIE21-02 – 2021.03
When the intake pressure value measured is lower than the setpoint in parameter “UN9”, the controller overrides capacity
reduction in the corresponding refrigerant circuit.
The capacity reduction override depends on the type and number of compressors featured in the circuit.
If only one compressor is fitted in the circuit and it is inverter controlled, capacity is reduced by the setpoint value stored in
parameter “UN14”. The value of parameter “UN13” in this case must be set to “100”.
If two compressors are fitted in the circuit and they are on-off type, capacity is reduced by the setpoint value stored in para
-
meter “UN13”. The correct value to set in parameter “UN13” to switch off one of the two compressors is “50”.
If the circuit is fitted with one inverter-controlled and one on-off compressor and capacity needs to be reduced in the inver
-
ter compressor, the value in parameter “UN13” must be set to “100” and the value in parameter “UN14” must be set at the
percentage value at which the inverter compressor is required to reduce its capacity. If capacity reduction is required to
switch off the on-off compressor and to bring the inverter compressor to the speed setpoint recorded in parameter “UN14”,
the value in parameter “UN13” must be set to “50” and the value in parameter “UN14” must be set at the percentage value
at which the inverter compressor is required to reduce its capacity.
Capacity reduction override in circuits featuring one on-off compressor only is not managed.
The capacity reduction override is stopped when the intake pressure is higher than the setpoint value in parameter “UN9”,
plus the value in parameter “UN10”, or after the time setpoint stored in parameter “UN17” has elapsed.
If the capacity reduction override is stopped after the time set in parameter “UN17”, but the condition persists for the time
set in parameter “UN18”, the override is restored.
Capacity reduction induced by high pressure probe
The controller offers the opportunity to override reduction capacity in the refrigerant circuit in order to limit the delivery pres -
sure and consequently prevent triggering alarms for high pressure in the circuit.
The parameters involved are shown in the table.
The values of the parameters are representative. In specific cases, different values can be set.
Parameter Value UM Description
UN5 37.00 bar High pressure - Prevention threshold
UN6 2.0 bar High pressure - Prevention differential
UN13 50 % Max. percentage limit in circuit 1 with capacity reduction
UN14 42 % Inverter scroll - Capacity reduction percentage override
UN15 50 % Max. percentage limit in circuit 2 with capacity reduction
UN17 2 min Capacity reduction activation time limit
UN18 2 min Time between two capacity reductions of the same circuit
A graphical representation of capacity reduction due to low pressure is shown below.
t
UN5
Hp
C2
UN6
UN17
Off
On
UN17 UN18
Off
On
C1
Fig. 23 Capacity reduction due to high pressure
3 Software functions