71 PB
Heating Mode
1. Start conditions:
When 24v compressor signal (Y) and 24v 4‑way valve signal (B) are received from the thermostat the unit will start heating.
2. Stopping operating in heating mode.
Stopping conditions:
When 0v compressor signal (Y) and 0v 4‑way valve signal (B) are received from the thermostat the unit will stop heating.
Stopping actions:
The compressor keeps operating with its current frequency, and detects its system pressure at the same time.
a. If the pressure keeps 522 PSI or more for 10 seconds, or it changes more than 14.5 PSI in 10 seconds, the compressor stops operating.
b. If the pressure changes less than 14.5 PSI in 10 seconds, the compressor keeps operating and the target pressure is set to decrease by 43.5 PSI
based on the current system pressure. The motor and electronic expansion valve are controlled as usual, the protection function and oil‑return
control are valid.
When the 24v compressor signal (Y) and 24v 4‑way valve signal (B) are received from the thermostat, the unit restores the normal target pressure
to operate or when the compressor has operated for 30 minutes with the decreased target pressure the unit stops operating.
Compressor running rules:
When the unit starts up in heating mode, the compressor starts to work, and
adjust its operating frequency according to the system target pressure and
the actual pressure. If the actual pressure is higher than the target pressure,
the compressor frequency will decrease; if the actual pressure is lower than
the target pressure, the compressor frequency increases; when the target
pressure is reached, the compressor frequency will keep stable.
Outdoor fan running rules:
Once the outdoor fan starts up, it will follow the rules below:
Single outdoor fan: First, it will run in an invariable speed for a short time;
Then it will regulate the speed by the saturation temperature (which is got
from high pressure cycling)
Double outdoor fan: If it has two outdoor fans, the upper fan regulates the
speed by the rules, and the low fan speed is slower than the upper fan speed
by 30 rpm~60 rpm.
Indoor Fan Running Rules
Unmatched system: Fan will operate according to fan setting on PCB.
Matched system: Fan will operate according to fan setting on PCB. RPM may
compensate for low‑load applications.
OPERATION
Control logic description
Figure 403
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