Service manual

15-8
CONTROL SYSTEM > GC 24
SM HADDCI 1-A.2 GB
15.4.12 Mode Setting
Mode defines the ODU operation mode. There are three possible operation modes:
STBY - standby mode
1.
COOL - the unit operating at cooling cycle2.
HEAT - the unit operating at heat pump cycle3.
The ODU define the system operation mode according to three methods set by the display key
board:
1. First request priority
The first IDU which requests different mode than STBY mode will set the new operation
mode. The mode will change once all the units exit the current operation mode.
2. Priority unit
If an IDU is defined as a priority unit, the operational mode will be defined according to that
unit request, unless the unit is at STBY mode.
In case priority unit is SB the mode will be set acceding to first request priority.
3. Forced operation mode
If forced mode is enabled than the ODU mode will be forced according to the Forced mode
input:
Open → COOL
Short → HEAT
The ODU will go to SB if all the IDU are at SB or at different modes.
4. SB Input
The ODU will change mode between COOL/HEAT and Idle according to the STBY dry
contact input as follows:
STBY input ODU mode
Short SB
Short -> Open last mode
Open according normal mode selection
15.4.13 Compressor Speed Control
15.4.13.1 Compressor Min On/Off time
Compressor minimum OFF time is MinOFFTime minutes except during Deicing protection. Compressor
minimum ON time is MinOnTime minutes, minimum ON time is ignored during protections, and when unit is
turned to STBY.
15.4.13.2 Compressor Speed calculation
During normal operation (excluding protections), the compressor speed is limited by the minimum speeds:
Min Speed Cool Max Speed Cool Min Speed Heat Max Speed Heat
15 75 15 95
15.4.13.3 Indoor Units NLOAD calculation
The NLOAD setting is done by the indoor unit controller, based on a PI control scheme. The actual NLOAD
to be sent to the outdoor unit controller is based on the preliminary LOAD calculation, the indoor fan speed,
and the power shedding function.
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