Panasonic U-72MF2U9 Service Manual page 19

3. Compressor Control
(3) Increasing/decreasing the heat exchanger capacity (when the outdoor unit heat exchanger is functioning as an
evaporator)
• Primarily when both the evaporation temperature (Te) and condensation temperature (Tc) are low
This occurs when the cooling capacity (heat intake) is high and the heating capacity (heat discharge) is low.
The outdoor heat exchanger capacity is increased, increasing the system evaporation capacity and raising
the evaporation temperature (Te). The amount of heat intake at the outdoor unit heat exchanger is increased,
increasing the heat discharge at the heating mode indoor units and raising the condensation temperature (Tc).
• Primarily when both the evaporation temperature (Te) and condensation temperature (Tc) are high
This occurs when the cooling capacity (heat intake) is low and the heating capacity (heat discharge) is high.
The outdoor heat exchanger capacity is decreased, decreasing the system evaporation capacity and lowering
the evaporation temperature (Te). The amount of heat intake at the outdoor unit heat exchanger is
decreased, decreasing the heat discharge at the heating mode indoor units and lowering the condensation
temperature (Tc).
Outdoor Heat Exchanger Control Table (when the outdoor heat exchanger is functioning as an evaporator)
A
42.8°F (6°C)
B
37.4°F (3°C)
30.2°F (-1°C)
C
26.6°F (-3°C)
24.8°F (-4°C)
3-7. Protection Control
3-7-1. Compressor discharge temperature protection
The compressor capacity is controlled according to the table below.
*Discharge temperature that is used for this control is the highest temperature among all compressors.
Discharge temp.
°F (°C)
222.8 106)
(
221.0 (105)
219.2 (104)
217.4 (103)
213.8 (101)
3-7-2. Abnormal low pressure protection
The compressor capacity is controlled according to the table below.
Low pressure
psi (MPa)
36.3 (0.25)
29.0 (0.20)
24.7 (0.17)
Low ← Condensation Temp. [Tc]
A
STAY
UP
Stop If this temperature is detected at regular intervals, alarm appears.
Capacity goes down 2.0 hp
Compressor
capacity
Capacity goes down 1.0 hp
decrease
Capacity goes down 0.5 hp
Compressor capacity increase prohibited
Compressor capacity increase possible
No restriction
Capacity goes up slowly
Capacity increase prohibited
Capacity goes down
→
B
C
DOWN
Target
STAY
1 - 11
3WAY VRF SYSTEM
Control Functions
High
D
hp = horsepower
1
2
3
4
5
6
7
8
9