Service Manual

Control Specification SiUS121502E
64 Function and Control
Parameters <Q value>
Indoor unit output determined from indoor unit volume, airflow rate and other factors.
<S value: Indoor Unit Capacity>
An S value is the capacity of the indoor unit, and is used for frequency command.
<∆D signal: Indoor frequency command>
The difference between the room thermistor temperature and the target temperature is recognized
as the ∆D signal and is used for frequency command.
Values depend on the type of indoor unit.
∗OFF = Thermostat OFF
Initial Frequency When starting the compressor, or when conditions are varied due to a change of operating rooms,
the frequency must be initialized according to a total of the maximum ∆D value of each room and a
total Q value (ΣQ) of the operating room (the room in which the thermostat is set to ON).
PI Control 1. P control
The Σ∆D value is calculated in each sampling time (20 seconds), and the frequency is adjusted
according to its difference from the frequency previously calculated.
2. I control
If the operating frequency does not change for more than a certain fixed time, the frequency is
adjusted according to the Σ∆D value.
When the Σ∆D value is low, the frequency is lowered.
When the Σ∆D value is high, the frequency is increased.
3. Limit of frequency increasing range
When the difference between the input current and the dropping value of the input current is
less than 1.5 A, the frequency increasing range must be limited.
4. Frequency control when other controls are functioning

When frequency is dropping;
Frequency control is carried out only when the frequency drops.

For limiting lower limit;
Frequency control is carried out only when the frequency rises.
5. Upper and lower limit of frequency by PI control
The frequency upper and lower limits are set according to the total of S values. When the indoor
unit quiet operation commands come from more than one room or when the outdoor unit quiet
operation commands come from all the rooms, the upper limit frequency is lower than the usual
setting.
Ex: Capacity S value Capacity S value
9 kBtu/h 25 18 kBtu/h 50
12 kBtu/h 35 24 kBtu/h 60
Temperature
difference
∆
D
signal
Temperature
difference
∆
D
signal
Temperature
difference
∆
D
signal
Temperature
difference
∆
D
signal
–2.0°C (–3.6°F) ∗OFF 0°C (0°F) 4 2.0°C (3.6°F) 8 4.0°C (7.2°F) C
–1.5°C (–2.7°F) 1 0.5°C (0.9°F) 5 2.5°C (4.5°F) 9 4.5°C (8.1°F) D
–1.0°C (–1.8°F) 2 1.0°C (1.8°F) 6 3.0°C (5.4°F) A 5.0°C (9°F) E
–0.5°C (–0.9°F) 3 1.5°C (2.7°F) 7 3.5°C (6.3°F) B 5.5°C (9.9°F) F