Service Manual

SiUS181631EA Branch Provider (BP) Unit Control
Functions and Control 71
6.3 SH Control in Cooling Operation
Outline This function ensures appropriate refrigerant distribution when many indoor units are operating in
cooling operation.
Details The heat exchanger temperatures and gas pipe temperatures of operating indoor units are
detected by the gas pipe thermistors, and the flow rates of the electronic expansion valve are
corrected so as to adjust the difference between the heat exchanger temperature and gas pipe
temperature of each indoor unit (hereafter referred to as SH) close to the target values.
When SH is higher than target value
→
Opens the valve of that indoor unit
When SH is lower than target value
→
Closes the valve of that indoor unit
When the liquid pipe temperature is lower than the heat exchanger temperature, the electronic
expansion valve is opened more than normal opening.
(Protection function to prevent rotor dew condensation)
The gas pipe temperature and indoor heat exchanger temperature are detected with a sampling
time of 40 seconds for the cooling SH control.
In order to prevent dew condensation in the connection pipe, the gas pipe lower-limit temperature is
set as follows.
Notes: 1. In SkyAir models, the indoor units are equipped with distribution capillary tubes; as a result, the
heat exchangers may superheat even when the condition is met.
2. In SkyAir models, the heat exchanger intermediate position is provided on the liquid connection
pipe side; as a result, superheated condition is difficult to detect.
(R19087)
Gas pipe lower limit temperature (˚C) = × outdoor temperature (˚C) – 17
240
256
(Gas pipe lower limit temperature (˚F) = × outdoor temperature (˚F) – 28.6)
Gas pipe lower limit temperature ≤ 8˚C (46.4˚F)
240
256
(˚C)(˚F)
–25
–20
–15
–10
–5
0
5
10
8
–13
–4
5
14
23
32
41
50
46.4
–5 0 5 10 15 20 25 30 35 40 45
Outdoor temperature
Gas pipe lower limit temperature
(˚C)
23 32 41 50 59 68 77 86 95 104 113 (˚F)