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6 Special Control
6.1 Outdoor Unit Duty Cycling
In systems with multiple outdoor units, outdoor unit duty cycling is used to prevent compressor burn out due to
unbalanced oil levels between outdoor units.
Timing of outdoor unit duty cycling:
After oil return operation.
On restart following compressor stop after set temperatures achieved.
Figure 3-6.1 shows an example of duty cycling in a system with 3 outdoor units.
Figure 3-6.1: Duty cycling in a system with 3 outdoor units
1
Notes:
1. The address settings on the outdoor unit main PCBs for “master unit”, “slave unit 1”, and “slave unit 2” do not change.
Startup control
Normal operation
After oil return operation or
after defrosting operation or
on restart following compressor
stop after set temperatures
achieved
Normal operation
Outdoor unit
duty cycling
Priority
1
Priority
2
Priority
3
Master Slave 1 Slave 2
Outdoor unit
duty cycling
Priority
3
Priority
1
Priority
2
Master Slave 1 Slave 2
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